Ruby native extension gems install fails - ruby

Question

When trying to install a ruby gem that uses native extensions my installs are failing.
Gem::Ext::BuildError: ERROR: Failed to build gem native extension.
The log file gives me the following output
"gcc-mp-4.9 -o conftest -I/Users/bigtunacan/.rvm/rubies/ruby-1.9.3-p551/include/ruby-1.9.1/x86_64-darwin13.4.0 -I/Users/bigtunacan/.rvm/rubies/ruby-1.9.3-p551/include/ruby-1.9.1/ruby/backward -I/Users/bigtunacan/.rvm/rubies/ruby-1.9.3-p551/include/ruby-1.9.1 -I. -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE -I/opt/local/include -O3 -ggdb -Wall -Wextra -Wno-unused-parameter -Wno-parentheses -Wno-long-long -Wno-missing-field-initializers -Wpointer-arith -Wwrite-strings -Wdeclaration-after-statement -Wimplicit-function-declaration -fno-common -pipe conftest.c -L. -L/Users/bigtunacan/.rvm/rubies/ruby-1.9.3-p551/lib -L/opt/local/lib -L. -L/opt/local/lib -lruby.1.9.1 -lpthread -ldl -lobjc "
checked program was:
/* begin */
1: #include "ruby.h"
2:
3: int main(int argc, char **argv)
4: {
5: return 0;
6: }
/* end */
It appears this is looking for a macports version of gcc instead of using the system gcc, but I don't even have any macports gcc installs on the system.
------ EDIT adding output from gem_make.out file ---------
/Users/bigtunacan/.rvm/rubies/ruby-1.9.3-p551/bin/ruby -r ./siteconf20160428-64282-8h2kw8.rb extconf.rb
checking for main() in -lcups... *** 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/bigtunacan/.rvm/rubies/ruby-1.9.3-p551/bin/ruby
--with-cupslib
--without-cupslib
/Users/bigtunacan/.rvm/rubies/ruby-1.9.3-p551/lib/ruby/1.9.1/mkmf.rb:381:in `try_do': The compiler failed to generate an executable file. (RuntimeError)
You have to install development tools first.
from /Users/bigtunacan/.rvm/rubies/ruby-1.9.3-p551/lib/ruby/1.9.1/mkmf.rb:461:in `try_link0'
from /Users/bigtunacan/.rvm/rubies/ruby-1.9.3-p551/lib/ruby/1.9.1/mkmf.rb:476:in `try_link'
from /Users/bigtunacan/.rvm/rubies/ruby-1.9.3-p551/lib/ruby/1.9.1/mkmf.rb:619:in `try_func'
from /Users/bigtunacan/.rvm/rubies/ruby-1.9.3-p551/lib/ruby/1.9.1/mkmf.rb:845:in `block in have_library'
from /Users/bigtunacan/.rvm/rubies/ruby-1.9.3-p551/lib/ruby/1.9.1/mkmf.rb:790:in `block in checking_for'
from /Users/bigtunacan/.rvm/rubies/ruby-1.9.3-p551/lib/ruby/1.9.1/mkmf.rb:284:in `block (2 levels) in postpone'
from /Users/bigtunacan/.rvm/rubies/ruby-1.9.3-p551/lib/ruby/1.9.1/mkmf.rb:254:in `open'
from /Users/bigtunacan/.rvm/rubies/ruby-1.9.3-p551/lib/ruby/1.9.1/mkmf.rb:284:in `block in postpone'
from /Users/bigtunacan/.rvm/rubies/ruby-1.9.3-p551/lib/ruby/1.9.1/mkmf.rb:254:in `open'
from /Users/bigtunacan/.rvm/rubies/ruby-1.9.3-p551/lib/ruby/1.9.1/mkmf.rb:280:in `postpone'
from /Users/bigtunacan/.rvm/rubies/ruby-1.9.3-p551/lib/ruby/1.9.1/mkmf.rb:789:in `checking_for'
from /Users/bigtunacan/.rvm/rubies/ruby-1.9.3-p551/lib/ruby/1.9.1/mkmf.rb:840:in `have_library'
from extconf.rb:3:in `<main>'
extconf failed, exit code 1

Answer 1

It ended up that the gcc setting is sticky in the rbconfig.rb file for the rvm gemset.
I had to go to
~/.rvm/rubies/ruby-1.9.3-p551/lib/ruby/1.9.1/x86_64-darwin13.4.0/rbconfig.rb
There I had to change
CONFIG["CC"] = "gcc-mp-4.9"
to
CONFIG["CC"] = "gcc"
and also change
CONFIG["configure_args"] = " '--prefix=/Users/bigtunacan/.rvm/rubies/ruby-1.9.3-p551' '--with-opt-dir=/opt/local' '--without-tcl' '--without-tk' '--disable-install-doc' '--enable-shared' 'CC=gcc-mp-4.9'"
to
CONFIG["configure_args"] = " '--prefix=/Users/bigtunacan/.rvm/rubies/ruby-1.9.3-p551' '--with-opt-dir=/opt/local' '--without-tcl' '--without-tk' '--disable-install-doc' '--enable-shared' 'CC=gcc'"