runtime/cgo: fix arm build, re-enable test

Fixes #4961.

R=golang-dev, r, minux.ma
CC=golang-dev
https://golang.org/cl/7443048

src/pkg/runtime/cgo/asm_arm.s

@@ -19,5 +19,5 @@ TEXT crosscall2(SB),7,$-4
 	MOVW	_cgo_load_gm(SB), R0
 	BL	(R0)
 	MOVW	PC, R14
-	MOVW	-4(R13), PC
+	MOVW	0(R13), PC
 	MOVM.IAW	(R13), [R0, R1, R2, R4, R5, R6, R7, R8, R9, R10, R11, R12, PC]

src/pkg/runtime/cgo/cgo_arm.c

+// Copyright 2013 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+#pragma cgo_import_static x_cgo_load_gm
+extern void x_cgo_load_gm(void);
+void (*_cgo_load_gm)(void) = x_cgo_load_gm;
+
+#pragma cgo_import_static x_cgo_save_gm
+extern void x_cgo_save_gm(void);
+void (*_cgo_save_gm)(void) = x_cgo_save_gm;
+

src/run.bash

@@ -75,7 +75,6 @@ go run $GOROOT/test/run.go - .
 
 [ "$CGO_ENABLED" != 1 ] ||
 [ "$GOHOSTOS" == openbsd ] || # issue 4878
-[ "$GOARCH" == arm ] || # issue 4961
 (xcd ../misc/cgo/test
 go test
 ) || exit $?