CONFIG_SITE for CPython wasm cross builds

config.site-wasm

#
# CONFIG_SITE=config.site-wasm READELF=true emconfigure ./configure -C --host=wasm32-unknown-emscripten --build=$(./config.guess) --without-pymalloc --enable-big-digits=30
# ln -sfr Modules/Setup.stdlib Modules/Setup.local
# emmake make CROSS_COMPILE=yes FREEZE_MODULE=../x86_64/Programs/_freeze_module PYTHON_FOR_BUILD=../x86_64/python _PYTHON_HOST_PLATFORM=wasm32-unknown-emscripten
#

# cannot be detected for cross builds
ac_cv_buggy_getaddrinfo=no
ac_cv_file__dev_ptmx=yes
ac_cv_file__dev_ptc=no

# new undefined symbols / unsupported features
ac_cv_func_posix_spawn=no
ac_cv_func_posix_spawnp=no
ac_cv_func_eventfd=no
ac_cv_func_memfd_create=no
ac_cv_func_prlimit=no

# unsupported syscall, https://github.com/emscripten-core/emscripten/issues/13393
ac_cv_func_shutdown=no

# The rest is based on pyodide
# https://github.com/pyodide/pyodide/blob/main/cpython/pyconfig.undefs.h

ac_cv_func_epoll=no
ac_cv_func_epoll_create1=no
ac_cv_header_linux_vm_sockets_h=no
ac_cv_func_socketpair=no
ac_cv_func_utimensat=no
ac_cv_func_sigaction=no

# Untested syscalls in emscripten
ac_cv_func_openat=no
ac_cv_func_mkdirat=no
ac_cv_func_fchownat=no
ac_cv_func_renameat=no
ac_cv_func_linkat=no
ac_cv_func_symlinkat=no
ac_cv_func_readlinkat=no
ac_cv_func_fchmodat=no
ac_cv_func_dup3=no

# Syscalls not implemented in emscripten
ac_cv_func_preadv2=no
ac_cv_func_preadv=no
ac_cv_func_pwritev2=no
ac_cv_func_pwritev=no
ac_cv_func_pipe2=no
ac_cv_func_nice=no

# Syscalls that resulted in a segfault
ac_cv_func_utimensat=no
ac_cv_header_sys_socket_h=no
ac_cv_header_sys_ioctl_h=no

# Unsupported functionality
#undef HAVE_PTHREAD_H