installing mysql2 gem on redhat - ruby

Question

Currently trying to install the mysql2 gem on redhat. This is what I'm getting after running gem install
gem install mysql2 -v 0.3.18 -- --with-mysql-config=/usr/bin/mysql_config
checking for ruby/thread.h... *** 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.
It looks like most people who get a similar error need to install mysql dev/lib packages. The packages are already installed and up to date. The mkmf.log file looks like this:
"gcc -o conftest -I/home/zdev/.rbenv/versions/2.2.0/include/ruby-2.2.0/x86_64-linux -I/home/zdev/.rbenv/versions/2.2.0/include/ruby-2.2.0/ruby/backward
-I/home/zdev/.rbenv/versions/2.2.0/include/ruby-2.2.0 -I. -I/home/zdev/.rbenv/versions/2.2.0/include -D_FILE_OFFSET_BITS=64 -O3 -fno-fast-math -ggdb3
-Wall -Wextra -Wno-unused-parameter -Wno-parentheses -Wno-long-long -Wno-missing-field-initializers -Wunused-variable -Wpointer-arith -Wwrite-strings
-Wdeclaration-after-statement -Wimplicit-function-declaration -Wdeprecated-declarations -Wno-packed-bitfield-compat conftest.c -L.
-L/home/zdev/.rbenv/versions/2.2.0/lib -Wl,-R/home/zdev/.rbenv/versions/2.2.0/lib -L/home/zdev/.rbenv/versions/2.2.0/lib -lruby-static -lpthread -lrt
-ldl -lcrypt -lm -lc"
In file included from /home/zdev/.rbenv/versions/2.2.0/include/ruby-2.2.0/ruby.h:33,
from conftest.c:1:
/home/zdev/.rbenv/versions/2.2.0/include/ruby-2.2.0/ruby/ruby.h:107: error: size of array 'ruby_check_sizeof_long' is negative
/home/zdev/.rbenv/versions/2.2.0/include/ruby-2.2.0/ruby/ruby.h:111: error: size of array 'ruby_check_sizeof_voidp' is negative
In file included from /home/zdorman/.rbenv/versions/2.2.0/include/ruby-2.2.0/ruby.h:33,
from conftest.c:1:
/home/zdev/.rbenv/versions/2.2.0/include/ruby-2.2.0/ruby/ruby.h: In function 'rb_int2num_inline':
/home/zdev/.rbenv/versions/2.2.0/include/ruby-2.2.0/ruby/ruby.h:1303: warning: comparison is always true due to limited range of data type
/home/zdev/.rbenv/versions/2.2.0/include/ruby-2.2.0/ruby/ruby.h:1303: warning: comparison is always true due to limited range of data type
/home/zdev/.rbenv/versions/2.2.0/include/ruby-2.2.0/ruby/ruby.h: In function 'rb_uint2num_inline':
/home/zdev/.rbenv/versions/2.2.0/include/ruby-2.2.0/ruby/ruby.h:1313: warning: comparison is always true due to limited range of data type
In file included from /home/zdorman/.rbenv/versions/2.2.0/include/ruby-2.2.0/ruby/intern.h:35,
from /home/zdorman/.rbenv/versions/2.2.0/include/ruby-2.2.0/ruby/ruby.h:1710,
from /home/zdorman/.rbenv/versions/2.2.0/include/ruby-2.2.0/ruby.h:33,
from conftest.c:1:
/home/zdev/.rbenv/versions/2.2.0/include/ruby-2.2.0/ruby/st.h: At top level:
/home/zdev/.rbenv/versions/2.2.0/include/ruby-2.2.0/ruby/st.h:52: error: size of array 'st_check_for_sizeof_st_index_t' is negative
checked program was:
/* begin */
1: #include "ruby.h"
2:
3: int main(int argc, char **argv)
4: {
5: return 0;
6: }
/* end */
The errors in the log file are produced by sanity checks like this:
typedef char ruby_check_sizeof_long[SIZEOF_LONG == sizeof(long) ? 1 : -1];
What could be the cause of this issue? gcc and mysql are both 64 bit - are there any other binaries/libs that would cause this issue?
For the record, there is a copy of the mysql2 gem already installed on this system. It was installed a couple years ago by the original developer, and is tied to a ruby install in /usr/bin. I'm trying to migrate a project over to using a ruby managed by rbenv. From a clean ruby install made through rbenv, bundle install will work flawlessly on our ubuntu box, but it trips up with the mysql2 gem on this system.