runtime: fix freebsd arm for hash change

Was missing definitions of open, read, close.

R=golang-dev
CC=golang-dev
https://golang.org/cl/7828043

src/pkg/runtime/sys_freebsd_arm.s

@@ -54,6 +54,20 @@ TEXT runtime·exit1(SB),7,$-8
 	MOVW.CS R9, (R9)
 	RET
 
+TEXT runtime·open(SB),7,$-8
+	MOVW 0(FP), R0	// arg 1 name
+	MOVW 4(FP), R1	// arg 2 mode
+	MOVW 8(FP), R2	// arg 3 perm
+	SWI $5
+	RET
+
+TEXT runtime·read(SB),7,$-8
+	MOVW 0(FP), R0	// arg 1 fd
+	MOVW 4(FP), R1	// arg 2 buf
+	MOVW 8(FP), R2	// arg 3 count
+	SWI $3
+	RET
+
 TEXT runtime·write(SB),7,$-8
 	MOVW 0(FP), R0	// arg 1 fd
 	MOVW 4(FP), R1	// arg 2 buf
@@ -61,6 +75,11 @@ TEXT runtime·write(SB),7,$-8
 	SWI $4
 	RET
 
+TEXT runtime·close(SB),7,$-8
+	MOVW 0(FP), R0	// arg 1 fd
+	SWI $6
+	RET
+
 TEXT runtime·getrlimit(SB),7,$-8
 	MOVW 0(FP), R0
 	MOVW 4(FP), R1