Retirado daqui:
The common predefined macros are GNU C extensions. They are available with the same meanings regardless of the machine or operating system on which you are using GNU C. Their names all start with double underscores.
__GNUC__
__GNUC_MINOR__
__GNUC_PATCHLEVEL__
These macros are defined by all GNU compilers that use the C preprocessor: C, C++, and [...]
