runtime: fix invalid pointer in windows/arm64 badsignal2

Initializes the R3 register with an available address in the stack. The addressed location is used to receive the number of bytes written by WriteFile.

Fixes golang#56080

Change-Id: I0368eb7a31d2d6a098fa9c26e074eb1114a92704
GitHub-Last-Rev: 23dbdb5
GitHub-Pull-Request: golang#56153
Reviewed-on: https://go-review.googlesource.com/c/go/+/442216
Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Cherry Mui <cherryyz@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>

src/runtime/sys_windows_arm64.s

@@ -113,7 +113,8 @@ TEXT runtime·badsignal2(SB),NOSPLIT,$16-0
 	MOVD	$runtime·badsignalmsg(SB), R1	// lpBuffer
 	MOVD	$runtime·badsignallen(SB), R2	// lpNumberOfBytesToWrite
 	MOVD	(R2), R2
-	MOVD	R13, R3		// lpNumberOfBytesWritten
+	// point R3 to stack local that will receive number of bytes written
+	ADD	$16, RSP, R3		// lpNumberOfBytesWritten
 	MOVD	$0, R4			// lpOverlapped
 	MOVD	runtime·_WriteFile(SB), R12
 	SUB	$16, RSP	// skip over saved frame pointer below RSP