Fix compiling graphlab HEAD against master on Macs

This pull request includes a couple of fixes to get OSX to compile graphlab. There were two main issues. First is that the cmake config was not properly testing for the `__builtin_ia32_crc32di` intrinsic (#19). This includes a patch to fix that test. Second, it fixes an issue where clang requires all functions to be declared before being used by a template function. Finally, it includes some minor fixes to silence some warnings and removes an executable bit turned on a header file.