gistfile1.txt

In file included from /home/mangix/devstuff/openwrt/staging_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/include/pthread.h:30,
                 from /home/mangix/devstuff/openwrt/build_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/gcc-9.3.0-final/mipsel-openwrt-linux-musl/libstdc++-v3/include/mipsel-openwrt-linux-musl/bits/gthr-default.h:35,
                 from /home/mangix/devstuff/openwrt/build_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/gcc-9.3.0-final/mipsel-openwrt-linux-musl/libstdc++-v3/include/mipsel-openwrt-linux-musl/bits/gthr.h:148,
                 from /home/mangix/devstuff/openwrt/build_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/gcc-9.3.0/libstdc++-v3/libsupc++/atexit_thread.cc:27:
/home/mangix/devstuff/openwrt/staging_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/include/sched.h:141:8: error: expected constructor, destructor, or type conversion before '(' token
  141 | __REDIR(sched_rr_get_interval, __sched_rr_get_interval_time64);
      |        ^
In file included from /home/mangix/devstuff/openwrt/staging_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/include/pthread.h:31,
                 from /home/mangix/devstuff/openwrt/build_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/gcc-9.3.0-final/mipsel-openwrt-linux-musl/libstdc++-v3/include/mipsel-openwrt-linux-musl/bits/gthr-default.h:35,
                 from /home/mangix/devstuff/openwrt/build_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/gcc-9.3.0-final/mipsel-openwrt-linux-musl/libstdc++-v3/include/mipsel-openwrt-linux-musl/bits/gthr.h:148,
                 from /home/mangix/devstuff/openwrt/build_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/gcc-9.3.0/libstdc++-v3/libsupc++/atexit_thread.cc:27:
/home/mangix/devstuff/openwrt/staging_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/include/time.h:134:8: error: expected constructor, destructor, or type conversion before '(' token
  134 | __REDIR(time, __time64);
      |        ^
/home/mangix/devstuff/openwrt/staging_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/include/time.h:135:8: error: expected constructor, destructor, or type conversion before '(' token
  135 | __REDIR(difftime, __difftime64);
      |        ^
/home/mangix/devstuff/openwrt/staging_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/include/time.h:136:8: error: expected constructor, destructor, or type conversion before '(' token
  136 | __REDIR(mktime, __mktime64);
      |        ^
/home/mangix/devstuff/openwrt/staging_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/include/time.h:137:8: error: expected constructor, destructor, or type conversion before '(' token
  137 | __REDIR(gmtime, __gmtime64);
      |        ^
/home/mangix/devstuff/openwrt/staging_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/include/time.h:138:8: error: expected constructor, destructor, or type conversion before '(' token
  138 | __REDIR(localtime, __localtime64);
      |        ^
/home/mangix/devstuff/openwrt/staging_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/include/time.h:139:8: error: expected constructor, destructor, or type conversion before '(' token
  139 | __REDIR(ctime, __ctime64);
      |        ^
/home/mangix/devstuff/openwrt/staging_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/include/time.h:140:8: error: expected constructor, destructor, or type conversion before '(' token
  140 | __REDIR(timespec_get, __timespec_get_time64);
      |        ^
/home/mangix/devstuff/openwrt/staging_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/include/time.h:144:8: error: expected constructor, destructor, or type conversion before '(' token
  144 | __REDIR(gmtime_r, __gmtime64_r);
      |        ^
/home/mangix/devstuff/openwrt/staging_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/include/time.h:145:8: error: expected constructor, destructor, or type conversion before '(' token
  145 | __REDIR(localtime_r, __localtime64_r);
      |        ^
/home/mangix/devstuff/openwrt/staging_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/include/time.h:146:8: error: expected constructor, destructor, or type conversion before '(' token
  146 | __REDIR(ctime_r, __ctime64_r);
      |        ^
/home/mangix/devstuff/openwrt/staging_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/include/time.h:147:8: error: expected constructor, destructor, or type conversion before '(' token
  147 | __REDIR(nanosleep, __nanosleep_time64);
      |        ^
/home/mangix/devstuff/openwrt/staging_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/include/time.h:148:8: error: expected constructor, destructor, or type conversion before '(' token
  148 | __REDIR(clock_getres, __clock_getres_time64);
      |        ^
/home/mangix/devstuff/openwrt/staging_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/include/time.h:149:8: error: expected constructor, destructor, or type conversion before '(' token
  149 | __REDIR(clock_gettime, __clock_gettime64);
      |        ^
/home/mangix/devstuff/openwrt/staging_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/include/time.h:150:8: error: expected constructor, destructor, or type conversion before '(' token
  150 | __REDIR(clock_settime, __clock_settime64);
      |        ^
/home/mangix/devstuff/openwrt/staging_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/include/time.h:151:8: error: expected constructor, destructor, or type conversion before '(' token
  151 | __REDIR(clock_nanosleep, __clock_nanosleep_time64);
      |        ^
/home/mangix/devstuff/openwrt/staging_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/include/time.h:152:8: error: expected constructor, destructor, or type conversion before '(' token
  152 | __REDIR(timer_settime, __timer_settime64);
      |        ^
/home/mangix/devstuff/openwrt/staging_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/include/time.h:153:8: error: expected constructor, destructor, or type conversion before '(' token
  153 | __REDIR(timer_gettime, __timer_gettime64);
      |        ^
/home/mangix/devstuff/openwrt/staging_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/include/time.h:156:8: error: expected constructor, destructor, or type conversion before '(' token
  156 | __REDIR(stime, __stime64);
      |        ^
/home/mangix/devstuff/openwrt/staging_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/include/time.h:157:8: error: expected constructor, destructor, or type conversion before '(' token
  157 | __REDIR(timegm, __timegm_time64);
      |        ^
In file included from /home/mangix/devstuff/openwrt/build_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/gcc-9.3.0-final/mipsel-openwrt-linux-musl/libstdc++-v3/include/mipsel-openwrt-linux-musl/bits/gthr-default.h:35,
                 from /home/mangix/devstuff/openwrt/build_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/gcc-9.3.0-final/mipsel-openwrt-linux-musl/libstdc++-v3/include/mipsel-openwrt-linux-musl/bits/gthr.h:148,
                 from /home/mangix/devstuff/openwrt/build_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/gcc-9.3.0/libstdc++-v3/libsupc++/atexit_thread.cc:27:
/home/mangix/devstuff/openwrt/staging_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/include/pthread.h:228:8: error: expected constructor, destructor, or type conversion before '(' token
  228 | __REDIR(pthread_mutex_timedlock, __pthread_mutex_timedlock_time64);
      |        ^
/home/mangix/devstuff/openwrt/staging_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/include/pthread.h:229:8: error: expected constructor, destructor, or type conversion before '(' token
  229 | __REDIR(pthread_cond_timedwait, __pthread_cond_timedwait_time64);
      |        ^
/home/mangix/devstuff/openwrt/staging_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/include/pthread.h:230:8: error: expected constructor, destructor, or type conversion before '(' token
  230 | __REDIR(pthread_rwlock_timedrdlock, __pthread_rwlock_timedrdlock_time64);
      |        ^
/home/mangix/devstuff/openwrt/staging_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/include/pthread.h:231:8: error: expected constructor, destructor, or type conversion before '(' token
  231 | __REDIR(pthread_rwlock_timedwrlock, __pthread_rwlock_timedwrlock_time64);
      |        ^
/home/mangix/devstuff/openwrt/staging_dir/toolchain-mipsel_24kc_gcc-9.3.0_musl/include/pthread.h:233:8: error: expected constructor, destructor, or type conversion before '(' token
  233 | __REDIR(pthread_timedjoin_np, __pthread_timedjoin_np_time64);
      |        ^
make[8]: *** [Makefile:761: atexit_thread.lo] Error 1

just run into something similar.
looks like missing __REDIR define for preprocessor
somewhat like this:
#define __REDIR(x,y) __typeof__(x) x __asm__(#y)

which was found in build_dir, but not in staging_dir
don't know what exactly happened, but I've managed to proceed further after manually added that define in
staging_dir/toolchain-${BOARD_TYPE}_gcc-9.3.0_musl/include/features.h

Oh I remember this now. musl’s features.h was patched illegitimately. I removed most of the custom files that were carried. This is most likely an issue with 18.06 and maybe 21.02.