runtime: check error codes for arm64 system calls

Unlike linux arm32, linux arm64 does not set the condition codes to indicate
whether a system call failed or not.  We must check if the return value
is in the error code range (the same as amd64 does).

Fixes runtime.TestBadOpen test.

Change-Id: I97a8b0a17b5f002a3215c535efa91d199cee3309
Reviewed-on: https://go-review.googlesource.com/9220Reviewed-by: Russ Cox <rsc@golang.org>

src/runtime/sys_linux_arm64.s

@@ -72,6 +72,7 @@ TEXT runtime·closefd(SB),NOSPLIT,$-8-12
 	MOVW	fd+0(FP), R0
 	MOVD	$SYS_close, R8
 	SVC
+	CMN	$4095, R0
 	BCC	done
 	MOVW	$-1, R0
 done:
@@ -84,6 +85,7 @@ TEXT runtime·write(SB),NOSPLIT,$-8-28
 	MOVW	n+16(FP), R2
 	MOVD	$SYS_write, R8
 	SVC
+	CMN	$4095, R0
 	BCC	done
 	MOVW	$-1, R0
 done:
@@ -96,6 +98,7 @@ TEXT runtime·read(SB),NOSPLIT,$-8-28
 	MOVW	n+16(FP), R2
 	MOVD	$SYS_read, R8
 	SVC
+	CMN	$4095, R0
 	BCC	done
 	MOVW	$-1, R0
 done: