Added -fno-common in order to fix OSX problem with common symbols

SOLUTION due to http://stackoverflow.com/questions/19398742/os-x-linker-unable-to-find-symbols-from-a-c-file-which-only-contains-variables
SEE ALSO: https://developer.apple.com/library/mac/documentation/developertools/conceptual/MachOTopics/1-Articles/executing_files.html