error_log

[~/Projects/surge]$ gem install eventmachine -v '1.2.3'                                                                                                                                                                                                 [master][ruby-2.4.1] 
Building native extensions.  This could take a while...
ERROR:  Error installing eventmachine:
	ERROR: Failed to build gem native extension.

    current directory: /Users/admin/.rvm/gems/ruby-2.4.1/gems/eventmachine-1.2.3/ext
/Users/admin/.rvm/rubies/ruby-2.4.1/bin/ruby -r ./siteconf20170821-20440-14nqfg8.rb extconf.rb
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers.  Check the mkmf.log file for more details.  You may
need configuration options.

Provided configuration options:
	--with-opt-dir
	--with-opt-include
	--without-opt-include=${opt-dir}/include
	--with-opt-lib
	--without-opt-lib=${opt-dir}/lib
	--with-make-prog
	--without-make-prog
	--srcdir=.
	--curdir
	--ruby=/Users/admin/.rvm/rubies/ruby-2.4.1/bin/$(RUBY_BASE_NAME)
	--with-ssl-dir
	--without-ssl-dir
	--with-ssl-include
	--without-ssl-include=${ssl-dir}/include
	--with-ssl-lib
	--without-ssl-lib=${ssl-dir}/lib
	--with-openssl-config
	--without-openssl-config
	--with-pkg-config
	--without-pkg-config
/Users/admin/.rvm/rubies/ruby-2.4.1/lib/ruby/2.4.0/mkmf.rb:457:in `try_do': The compiler failed to generate an executable file. (RuntimeError)
You have to install development tools first.
	from /Users/admin/.rvm/rubies/ruby-2.4.1/lib/ruby/2.4.0/mkmf.rb:542:in `try_link0'
	from /Users/admin/.rvm/rubies/ruby-2.4.1/lib/ruby/2.4.0/mkmf.rb:557:in `try_link'
	from /Users/admin/.rvm/rubies/ruby-2.4.1/lib/ruby/2.4.0/mkmf.rb:658:in `try_ldflags'
	from /Users/admin/.rvm/rubies/ruby-2.4.1/lib/ruby/2.4.0/mkmf.rb:1818:in `pkg_config'
	from extconf.rb:65:in `pkg_config_wrapper'
	from extconf.rb:92:in `<main>'

To see why this extension failed to compile, please check the mkmf.log which can be found here:

  /Users/admin/.rvm/gems/ruby-2.4.1/extensions/x86_64-darwin-15/2.4.0/eventmachine-1.2.3/mkmf.log

extconf failed, exit code 1

Gem files will remain installed in /Users/admin/.rvm/gems/ruby-2.4.1/gems/eventmachine-1.2.3 for inspection.
Results logged to /Users/admin/.rvm/gems/ruby-2.4.1/extensions/x86_64-darwin-15/2.4.0/eventmachine-1.2.3/gem_make.out

log

"gcc -o conftest -I/Users/admin/.rvm/rubies/ruby-2.4.1/include/ruby-2.4.0/x86_64-darwin15 -I/Users/admin/.rvm/rubies/ruby-2.4.1/include/ruby-2.4.0/ruby/backward -I/Users/admin/.rvm/rubies/ruby-2.4.1/include/ruby-2.4.0 -I.  -I/usr/local/opt/libyaml/include -I/usr/local/opt/readline/include -I/usr/local/opt/libksba/include -I/usr/local/opt/[email protected]/include -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE -D_DARWIN_UNLIMITED_SELECT -D_REENTRANT   -O3 -fno-fast-math -ggdb3 -Wall -Wextra -Wno-unused-parameter -Wno-parentheses -Wno-long-long -Wno-missing-field-initializers -Wno-tautological-compare -Wno-parentheses-equality -Wno-constant-logical-operand -Wno-self-assign -Wunused-variable -Wimplicit-int -Wpointer-arith -Wwrite-strings -Wdeclaration-after-statement -Wshorten-64-to-32 -Wimplicit-function-declaration -Wdivision-by-zero -Wdeprecated-declarations -Wextra-tokens  -fno-common -pipe conftest.c  -L. -L/Users/admin/.rvm/rubies/ruby-2.4.1/lib -L/usr/local/opt/libyaml/lib -L/usr/local/opt/readline/lib -L/usr/local/opt/libksba/lib -L/usr/local/opt/[email protected]/lib -L. -fstack-protector -L/usr/local/lib -L/usr/local/opt/libyaml/lib -L/usr/local/opt/readline/lib -L/usr/local/opt/libksba/lib -L/usr/local/opt/[email protected]/lib     -lruby.2.4.1  -lpthread -ldl -lobjc "
xcrun: error: invalid active developer path (/Library/Developer/CommandLineTools), missing xcrun at: /Library/Developer/CommandLineTools/usr/bin/xcrun
checked program was:
/* begin */
1: #include "ruby.h"
2: 
3: int main(int argc, char **argv)
4: {
5:   return 0;
6: }
/* end */

"pkg-config --exists openssl"
| pkg-config --libs openssl
=> "-lssl -lcrypto -lz\n"