s390x: only build kernels supported by gcc with dynamic arch support

When building with dynamic arch support, only build kernels for
architectures that are supported by the gcc we are building with.

Signed-off-by: Marius Hillenbrand <mhillen@linux.ibm.com>

Makefile.system

@@ -564,8 +564,26 @@ endif
 
 ifeq ($(ARCH), zarch)
 DYNAMIC_CORE = ZARCH_GENERIC
+
+# Z13 is supported since gcc-5.2, gcc-6, and in RHEL 7.3 and newer
+GCC_GE_52 := $(subst 0,,$(shell expr `$(CC) -dumpversion` \>= "5.2"))
+
+ifeq ($(wildcard /etc/redhat-release), /etc/redhat-release)
+RHEL_WITH_Z13 := $(subst 0,,$(shell source /etc/os-release ; expr $$VERSION_ID \>= "7.3"))
+endif
+
+ifeq ($(or $(GCC_GE_52),$(RHEL_WITH_Z13)), 1)
 DYNAMIC_CORE += Z13
+else
+$(info OpenBLAS: Not building Z13 kernels because gcc is older than 5.2 or 6.x)
+endif
+
+GCC_MAJOR_GE_7 := $(shell expr `$(CC) -dumpversion | cut -f1 -d.` \>= 7)
+ifeq ($(GCC_MAJOR_GE_7), 1)
 DYNAMIC_CORE += Z14
+else
+$(info OpenBLAS: Not building Z14 kernels because gcc is older than 7.x)
+endif
 endif
 
 ifeq ($(ARCH), power)