Enables the GNU compiler extensions that the ARM compiler supports.
The version of GCC the extensions are compatible with can be determined by inspecting the predefined macros __GNUC__ and __GNUC_MINOR__.
In addition, in GNU mode, the ARM compiler emulates GCC in its conformance to the C/C++ standards, whether more or less strict.
This option can also be combined with other source language command-line options. For example, armcc --c90 --gnu.