Add AVX flags for clang/aocc as well

Author: martin-frbg

Makefile.x86_64

@@ -78,6 +78,10 @@ GCCMINORVERSIONGTEQ7 := $(shell expr `$(CC) -dumpversion | cut -f2 -d.` \>= 7)
 ifeq ($(GCCVERSIONGTEQ4)$(GCCMINORVERSIONGTEQ7), 11)
 CCOMMON_OPT += -mavx2
 endif
+else 
+ifeq ($(C_COMPILER), CLANG)
+CCOMMON_OPT += -mavx2
+endif
 endif
 ifeq ($(F_COMPILER), GFORTRAN)
 # AVX2 support was added in 4.7.0