internal/cpu: use #ifdef __s390x__ in C code

Patch by Jakub Jelinek.

Fixes https://gcc.gnu.org/PR89407

Change-Id: I985210bdd58940d0c082073d6fbc2c312632376a
Reviewed-on: https://go-review.googlesource.com/c/163297
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/libgo/go/internal/cpu/cpu_gccgo.c b/libgo/go/internal/cpu/cpu_gccgo.c
index 6908d34..ed0e7bf 100644
--- a/libgo/go/internal/cpu/cpu_gccgo.c
+++ b/libgo/go/internal/cpu/cpu_gccgo.c
@@ -71,7 +71,7 @@
 
 #endif /* defined(__i386__) || defined(__x86_64__)  */
 
-#ifdef __s390__
+#ifdef __s390x__
 
 struct facilityList {
 	uint64_t bits[4];
@@ -184,4 +184,4 @@
     return ret;
 }
 
-#endif /* defined(__s390__)  */
+#endif /* defined(__s390x__)  */