runtime: fix build for non-split-stack systems

Change memory allocation accounting for stacks to use stacks_sys,
    since that seems to be what it is for.
    
    Reviewed-on: https://go-review.googlesource.com/43297

From-SVN: r247967

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-3c1258156a2ae483c5cc523cb7a3c3374cbe7c2c
+d5bfa6cebb19a154cbfbc53f6e647d2ca7adef68
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/go/runtime/runtime2.go

@@ -793,3 +793,10 @@ type g_ucontext_t [(_sizeof_ucontext_t + 15) / unsafe.Sizeof(uintptr(0))]uintptr
 // sigset is the Go version of the C type sigset_t.
 // _sigset_t is defined by the Makefile from <signal.h>.
 type sigset _sigset_t
+
+// getMemstats returns a pointer to the internal memstats variable,
+// for C code.
+//go:linkname getMemstats runtime.getMemstats
+func getMemstats() *mstats {
+	return &memstats
+}

libgo/runtime/proc.c

@@ -406,6 +406,8 @@ extern void globrunqput(G*)
   __asm__(GOSYM_PREFIX "runtime.globrunqput");
 extern P* pidleget(void)
   __asm__(GOSYM_PREFIX "runtime.pidleget");
+extern struct mstats* getMemstats(void)
+  __asm__(GOSYM_PREFIX "runtime.getMemstats");
 
 bool runtime_isstarted;
 
@@ -726,7 +728,7 @@ runtime_malg(bool allocatestack, bool signalstack, byte** ret_stack, uintptr* re
                 // 32-bit mode, the Go allocation space is all of
                 // memory anyhow.
 		if(sizeof(void*) == 8) {
-			void *p = runtime_sysAlloc(stacksize, &mstats()->other_sys);
+			void *p = runtime_sysAlloc(stacksize, &getMemstats()->stacks_sys);
 			if(p == nil)
 				runtime_throw("runtime: cannot allocate memory for goroutine stack");
 			*ret_stack = (byte*)p;

libgo/runtime/stack.c

@@ -80,7 +80,6 @@ static void doscanstack1(G *gp, void *gcw) {
 			scanstackblock(sp, (uintptr)(spsize), gcw);
 	}
 #else
-	M *mp;
 	byte* bottom;
 	byte* top;