runtime: use 64-bit negative error code on 64-bit machines

NEGL does a negation of the bottom 32 bits and then zero-extends to 64 bits,
resulting in a negative 32-bit number but a positive 64-bit number.

NEGQ does a full 64-bit negation, so that the result is negative both as
a 32-bit and as a 64-bit number.

This doesn't matter for the functions that are declared to return int32.
It only matters for the ones that return int64 or void* [sic].

This will fix the current incorrect error in the OpenBSD/amd64 build.
The build will still be broken, but it won't report a bogus error.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/7536046

src/pkg/runtime/sys_darwin_amd64.s

@@ -289,7 +289,7 @@ TEXT runtime·bsdthread_create(SB),7,$0
 	MOVQ	$(0x2000000+360), AX	// bsdthread_create
 	SYSCALL
 	JCC 3(PC)
-	NEGL	AX
+	NEGQ	AX
 	RET
 	MOVL	$0, AX
 	RET
@@ -342,7 +342,7 @@ TEXT runtime·bsdthread_register(SB),7,$0
 	MOVQ	$(0x2000000+366), AX	// bsdthread_register
 	SYSCALL
 	JCC 3(PC)
-	NEGL	AX
+	NEGQ	AX
 	RET
 	MOVL	$0, AX
 	RET
@@ -435,7 +435,7 @@ TEXT runtime·sysctl(SB),7,$0
 	MOVL	$(0x2000000+202), AX	// syscall entry
 	SYSCALL
 	JCC 3(PC)
-	NEGL	AX
+	NEGQ	AX
 	RET
 	MOVL	$0, AX
 	RET
@@ -448,7 +448,7 @@ TEXT runtime·kqueue(SB),7,$0
 	MOVL	$(0x2000000+362), AX
 	SYSCALL
 	JCC	2(PC)
-	NEGL	AX
+	NEGQ	AX
 	RET
 
 // int32 runtime·kevent(int kq, Kevent *changelist, int nchanges, Kevent *eventlist, int nevents, Timespec *timeout);
@@ -462,7 +462,7 @@ TEXT runtime·kevent(SB),7,$0
 	MOVL	$(0x2000000+363), AX
 	SYSCALL
 	JCC	2(PC)
-	NEGL	AX
+	NEGQ	AX
 	RET
 
 // void runtime·closeonexec(int32 fd);

src/pkg/runtime/sys_freebsd_amd64.s

@@ -261,7 +261,7 @@ TEXT runtime·sysctl(SB),7,$0
 	MOVQ	$202, AX		// sys___sysctl
 	SYSCALL
 	JCC 3(PC)
-	NEGL	AX
+	NEGQ	AX
 	RET
 	MOVL	$0, AX
 	RET

src/pkg/runtime/sys_netbsd_amd64.s

@@ -16,7 +16,7 @@ TEXT runtime·lwp_create(SB),7,$0
 	MOVL	$309, AX		// sys__lwp_create
 	SYSCALL
 	JCC	2(PC)
-	NEGL	AX
+	NEGQ	AX
 	RET
 
 TEXT runtime·lwp_tramp(SB),7,$0
@@ -254,7 +254,7 @@ TEXT runtime·mmap(SB),7,$0
 	MOVL	$197, AX		// sys_mmap
 	SYSCALL
 	JCC	2(PC)
-	NEGL	AX
+	NEGQ	AX
 	ADDQ	$16, SP
 	RET
 
@@ -306,7 +306,7 @@ TEXT runtime·sysctl(SB),7,$0
 	MOVQ	$202, AX		// sys___sysctl
 	SYSCALL
 	JCC 3(PC)
-	NEGL	AX
+	NEGQ	AX
 	RET
 	MOVL	$0, AX
 	RET

src/pkg/runtime/sys_openbsd_amd64.s

@@ -23,7 +23,7 @@ TEXT runtime·tfork(SB),7,$32
 
 	// Return if tfork syscall failed.
 	JCC	3(PC)
-	NEGL	AX
+	NEGQ	AX
 	RET
 
 	// In parent, return.
@@ -243,7 +243,7 @@ TEXT runtime·mmap(SB),7,$0
 	MOVL	$197, AX
 	SYSCALL
 	JCC	2(PC)
-	NEGL	AX
+	NEGQ	AX
 	ADDQ	$16, SP
 	RET
 
@@ -294,7 +294,7 @@ TEXT runtime·sysctl(SB),7,$0
 	MOVQ	$202, AX		// sys___sysctl
 	SYSCALL
 	JCC	3(PC)
-	NEGL	AX
+	NEGQ	AX
 	RET
 	MOVL	$0, AX
 	RET