runtime: remove non-extern decls of runtime.goarm

The linker is in charge of providing the one true declaration.

R=golang-dev, dave, r
CC=golang-dev
https://golang.org/cl/39560043

src/cmd/5l/obj.c

@@ -95,6 +95,6 @@ archinit(void)
 
 	// embed goarm to runtime.goarm
 	s = linklookup(ctxt, "runtime.goarm", 0);
-	s->dupok = 1;
+	s->type = SRODATA;
 	adduint8(ctxt, s, goarm);
 }

src/pkg/runtime/asm_arm.s

@@ -89,8 +89,6 @@ TEXT runtime·breakpoint(SB),NOSPLIT,$0-0
 	WORD	$0xe1200071	// BKPT 0x0001
 	RET
 
-GLOBL runtime·goarm(SB), $4
-
 TEXT runtime·asminit(SB),NOSPLIT,$0-0
 	// disable runfast (flush-to-zero) mode of vfp if runtime.goarm > 5
 	MOVW	runtime·goarm(SB), R11

src/pkg/runtime/os_linux_arm.c

@@ -16,7 +16,7 @@
 static uint32 runtime·randomNumber;
 uint8  runtime·armArch = 6;	// we default to ARMv6
 uint32 runtime·hwcap;	// set by setup_auxv
-uint8  runtime·goarm;	// set by 5l
+extern uint8  runtime·goarm;	// set by 5l
 
 void
 runtime·checkgoarm(void)