Use GCC/Clang "-std=c99" flag instead of "-std=gnu99" in rockspec
Use GCC/Clang "-std=c99" flag instead of "-std=gnu99" in rockspec

The "gnu99" option enables GNUC/POSIX/XOPEN extensions that aren't
needed by the library code.

craigbarnes/lua-gumbo,craigbarnes/lua-gumbo,craigbarnes/lua-gumbo