[release-branch.go1.24] runtime: fix usleep on s390x/linux

The timespec argument takes the remainder in nanoseconds, not
microseconds. Convert the remaining time to nsec.

Fixes #71728

Change-Id: I36cbbe3a088830c5e3afcc9516ef42e96ee21268
Reviewed-on: https://go-review.googlesource.com/c/go/+/648915
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Mauri de Souza Meneguzzo <[email protected]>
Reviewed-by: Axel Busch <[email protected]>
Run-TryBot: Paul Murphy <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Vishwanatha HD <[email protected]>
Reviewed-on: https://go-review.googlesource.com/c/go/+/649375
Auto-Submit: Ian Lance Taylor <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: pmur

src/runtime/sys_linux_s390x.s

@@ -112,9 +112,10 @@ TEXT runtime·usleep(SB),NOSPLIT,$16-4
 	MOVW	$1000000, R3
 	DIVD	R3, R2
 	MOVD	R2, 8(R15)
-	MOVW	$1000, R3
-	MULLD	R2, R3
+	MULLD	R2, R3		// Convert sec to usec and subtract
 	SUB	R3, R4
+	MOVW	$1000, R3
+	MULLD	R3, R4		// Convert remaining usec into nsec.
 	MOVD	R4, 16(R15)
 
 	// nanosleep(&ts, 0)