darwin, freebsd: ignore write failure (during print, panic)

The other operating systems already ignore write failures.

Fixes #1279.

R=r, r2
CC=golang-dev
https://golang.org/cl/3723041

src/pkg/runtime/darwin/386/sys.s

@@ -31,8 +31,6 @@ TEXT runtime·exit1(SB),7,$0
 TEXT runtime·write(SB),7,$0
 	MOVL	$4, AX
 	INT	$0x80
-	JAE	2(PC)
-	CALL	runtime·notok(SB)
 	RET
 
 TEXT runtime·mmap(SB),7,$0

src/pkg/runtime/darwin/amd64/sys.s

@@ -36,8 +36,6 @@ TEXT runtime·write(SB),7,$0
 	MOVL	24(SP), DX		// arg 3 count
 	MOVL	$(0x2000000+4), AX	// syscall entry
 	SYSCALL
-	JCC	2(PC)
-	CALL	runtime·notok(SB)
 	RET
 
 // void gettime(int64 *sec, int32 *usec)

src/pkg/runtime/freebsd/386/sys.s

@@ -58,8 +58,6 @@ TEXT runtime·exit1(SB),7,$-4
 TEXT runtime·write(SB),7,$-4
 	MOVL	$4, AX
 	INT	$0x80
-	JAE	2(PC)
-	CALL	runtime·notok(SB)
 	RET
 
 TEXT runtime·notok(SB),7,$0

src/pkg/runtime/freebsd/amd64/sys.s

@@ -63,8 +63,6 @@ TEXT runtime·write(SB),7,$-8
 	MOVL	24(SP), DX		// arg 3 count
 	MOVL	$4, AX
 	SYSCALL
-	JCC	2(PC)
-	CALL	runtime·notok(SB)
 	RET
 
 TEXT runtime·gettime(SB), 7, $32