make march=cooperlake option conditional on gcc >= 10.1

Makefile.x86_64

@@ -30,8 +30,15 @@ endif
 ifeq ($(CORE), COOPERLAKE)
 ifndef DYNAMIC_ARCH
 ifndef NO_AVX512
+ifeq ($(C_COMPILER), GCC)
+# cooperlake support was added in 10.1
+GCCVERSIONGTEQ10 := $(shell expr `$(CC) -dumpversion | cut -f1 -d.` \>= 10)
+GCCMINORVERSIONGTEQ1 := $(shell expr `$(CC) -dumpversion | cut -f2 -d.` \>= 1)
+ifeq ($(GCCVERSIONGTEQ10)$(GCCMINORVERSIONGTEQ1), 11)
 CCOMMON_OPT += -march=cooperlake
 FCOMMON_OPT += -march=cooperlake
+endif
+endif
 ifeq ($(OSNAME), CYGWIN_NT)
 CCOMMON_OPT += -fno-asynchronous-unwind-tables
 FCOMMON_OPT += -fno-asynchronous-unwind-tables