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.

Makefile.power

@@ -17,6 +17,7 @@ endif
 ifeq ($(CORE), POWER9)
 ifneq ($(C_COMPILER), PGI)
 CCOMMON_OPT += -Ofast -mvsx -fno-fast-math
+ifeq ($(C_COMPILER), GCC)
 ifneq ($(GCCVERSIONGT4), 1)
 $(warning your compiler is too old to fully support POWER9, getting a newer version of gcc is recommended)
 CCOMMON_OPT += -mcpu=power8 -mtune=power8 
@@ -24,10 +25,14 @@ else
 CCOMMON_OPT += -mcpu=power9 -mtune=power9 
 endif
 else
+CCOMMON_OPT += -mcpu=power9 -mtune=power9
+endif
+else
 CCOMMON_OPT += -fast -Mvect=simd -Mcache_align
 endif
 ifneq ($(F_COMPILER), PGI)
 FCOMMON_OPT += -O2 -frecursive -fno-fast-math
+ifeq ($(C_COMPILER), GCC)
 ifneq ($(GCCVERSIONGT4), 1)
 $(warning your compiler is too old to fully support POWER9, getting a newer version of gcc is recommended)
 FCOMMON_OPT += -mcpu=power8 -mtune=power8 
@@ -35,6 +40,9 @@ else
 FCOMMON_OPT += -mcpu=power9 -mtune=power9 
 endif
 else
+FCOMMON_OPT += -mcpu=power9 -mtune=power9
+endif
+else
 FCOMMON_OPT += -O2 -Mrecursive
 endif
 endif