POWER9: Fix mcpu option with clang
POWER9: Fix mcpu option with clang

Adding check for compiler type before checking GCC version in Makefile.
This allows clang to use power9 instead of power8 when CORE is POWER9.

xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS