runtime: fix linux/amd64p32 build

Implement runtime.atomicand8 for amd64p32 which was overlooked
in CL 7861.

Change-Id: Ic7eccddc6fd6c4682cac1761294893928f5428a2
Reviewed-on: https://go-review.googlesource.com/7920Reviewed-by: Minux Ma <minux@golang.org>

src/runtime/asm_amd64p32.s

@@ -541,6 +541,14 @@ TEXT runtime·atomicor8(SB), NOSPLIT, $0-5
 	ORB	AX, 0(BX)
 	RET
 
+// void	runtime·atomicand8(byte volatile*, byte);
+TEXT runtime·atomicand8(SB), NOSPLIT, $0-5
+	MOVL	ptr+0(FP), BX
+	MOVB	val+4(FP), AX
+	LOCK
+	ANDB	AX, 0(BX)
+	RET
+
 // void jmpdefer(fn, sp);
 // called from deferreturn.
 // 1. pop the caller