internal/cpu: add aarch64 support functions

Patch from Andreas Schwab.

Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/281000

gcc/go/gofrontend/MERGE

-fa161cb71880cf80ef53fb4bf35dba8ee01af648
+2b5bdd22b7ec2fc13ae0f644c781f64c1a209500
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/go/internal/cpu/cpu_gccgo.c

@@ -200,3 +200,29 @@ struct queryResult kdsaQuery() {
 }
 
 #endif /* defined(__s390x__)  */
+
+#ifdef __aarch64__
+
+uint64_t getisar0(void)
+  __asm__(GOSYM_PREFIX "internal_1cpu.getisar0")
+  __attribute__((no_split_stack));
+
+uint64_t getisar0() {
+       uint64_t isar0;
+
+       __asm__("mrs %0,id_aa64isar0_el1" : "=r"(isar0));
+       return isar0;
+}
+
+uint64_t getMIDR(void)
+  __asm__(GOSYM_PREFIX "internal_1cpu.getMIDR")
+  __attribute__((no_split_stack));
+
+uint64_t getMIDR() {
+       uint64_t MIDR;
+
+       __asm__("mrs %0,midr_el1" : "=r"(MIDR));
+       return MIDR;
+}
+
+#endif /* defined(__aarch64__) */