runtime: mark all runtime.cputicks implementations NOSPLIT

Fixes #10450

runtime.cputicks is called from runtime.exitsyscall and must not
split the stack. cputicks is implemented in several ways and the
NOSPLIT annotation was missing from a few of these.

Change-Id: I5cbbb4e5888c5d298fe2fef240782d0e49f59af8
Reviewed-on: https://go-review.googlesource.com/8939
Reviewed-by: Aram Hăvărneanu <aram@mgk.ro>

src/runtime/os_linux_arm.go

@@ -64,6 +64,7 @@ func sysargs(argc int32, argv **byte) {
 	}
 }
 
+//go:nosplit
 func cputicks() int64 {
 	// Currently cputicks() is used in blocking profiler and to seed fastrand1().
 	// nanotime() is a poor approximation of CPU ticks that is enough for the profiler.

src/runtime/os_linux_arm64.go

@@ -11,6 +11,7 @@ const (
 
 var randomNumber uint32
 
+//go:nosplit
 func cputicks() int64 {
 	// Currently cputicks() is used in blocking profiler and to seed fastrand1().
 	// nanotime() is a poor approximation of CPU ticks that is enough for the profiler.