runtime: always initialise procid on netbsd

The correct procid is needed for unparking LWPs on NetBSD - always
initialise procid in minit() so that cgo works correctly. The non-cgo
case already works correctly since procid is initialised via
lwp_create().

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/6257071

src/pkg/runtime/sys_netbsd_386.s

@@ -292,6 +292,11 @@ TEXT runtime·lwp_unpark(SB),7,$-4
 	INT	$0x80
 	RET
 
+TEXT runtime·lwp_self(SB),7,$-4
+	MOVL	$311, AX		// sys__lwp_self
+	INT	$0x80
+	RET
+
 TEXT runtime·sysctl(SB),7,$28
 	LEAL	arg0+0(FP), SI
 	LEAL	4(SP), DI

src/pkg/runtime/sys_netbsd_amd64.s

@@ -61,6 +61,11 @@ TEXT runtime·lwp_unpark(SB),7,$0
 	SYSCALL
 	RET
 
+TEXT runtime·lwp_self(SB),7,$0
+	MOVL	$311, AX		// sys__lwp_self
+	SYSCALL
+	RET
+
 // Exit the entire program (like C exit)
 TEXT runtime·exit(SB),7,$-8
 	MOVL	8(SP), DI		// arg 1 - exit status

src/pkg/runtime/thread_netbsd.c

@@ -28,6 +28,7 @@ extern int32 runtime·lwp_create(UcontextT *context, uintptr flags, void *lwpid)
 extern void runtime·lwp_mcontext_init(void *mc, void *stack, M *m, G *g, void (*fn)(void));
 extern int32 runtime·lwp_park(Timespec *abstime, int32 unpark, void *hint, void *unparkhint);
 extern int32 runtime·lwp_unpark(int32 lwp, void *hint);
+extern int32 runtime·lwp_self(void);
 
 // From NetBSD's <sys/sysctl.h>
 #define	CTL_HW	6
@@ -181,9 +182,6 @@ void
 runtime·osinit(void)
 {
 	runtime·ncpu = getncpu();
-
-	// Main thread is always LWP 1.
-	m->procid = 1;
 }
 
 void
@@ -196,6 +194,8 @@ runtime·goenvs(void)
 void
 runtime·minit(void)
 {
+	m->procid = runtime·lwp_self();
+
 	// Initialize signal handling
 	m->gsignal = runtime·malg(32*1024);
 	runtime·signalstack((byte*)m->gsignal->stackguard - StackGuard, 32*1024);