runtime: add support for linux/arm64

Change-Id: Ibda6a5bedaff57fd161d63fc04ad260931d34413
Reviewed-on: https://go-review.googlesource.com/7142
Reviewed-by: Russ Cox <rsc@golang.org>
diff --git a/src/runtime/traceback.go b/src/runtime/traceback.go
index c7e3b0b..9db5faf 100644
--- a/src/runtime/traceback.go
+++ b/src/runtime/traceback.go
@@ -357,6 +357,10 @@
 		if usesLR && waspanic {
 			x := *(*uintptr)(unsafe.Pointer(frame.sp))
 			frame.sp += ptrSize
+			if GOARCH == "arm64" {
+				// arm64 needs 16-byte aligned SP, always
+				frame.sp += ptrSize
+			}
 			f = findfunc(frame.pc)
 			frame.fn = f
 			if f == nil {