time: record monotonic clock reading in time.Now, for more accurate comparisons

See https://golang.org/design/12914-monotonic for details.

Fixes #12914.

Change-Id: I80edc2e6c012b4ace7161c84cf067d444381a009
Reviewed-on: https://go-review.googlesource.com/36255
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Caleb Spare <cespare@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/src/runtime/sys_plan9_386.s b/src/runtime/sys_plan9_386.s
index 41aa2fd..6baa813 100644
--- a/src/runtime/sys_plan9_386.s
+++ b/src/runtime/sys_plan9_386.s
@@ -102,8 +102,8 @@
 	MOVL	$-1, ret_hi+8(FP)
 	RET
 
-// func now() (sec int64, nsec int32)
-TEXT time·now(SB),NOSPLIT,$8-12
+// func walltime() (sec int64, nsec int32)
+TEXT runtime·walltime(SB),NOSPLIT,$8-12
 	CALL	runtime·nanotime(SB)
 	MOVL	0(SP), AX
 	MOVL	4(SP), DX