runtime: fix plan9/windows build

Fix few remaining cases after cl/117580043.

TBR=dfc
R=golang-codereviews
CC=dave, golang-codereviews
https://golang.org/cl/124850043

src/pkg/runtime/callback_windows.c

@@ -60,7 +60,7 @@ runtime·compilecallback(Eface fn, bool cleanstack)
 	}
 	if(n >= cb_max)
 		runtime·throw("too many callback functions");
-	c = runtime·mal(sizeof *c);
+	c = runtime·mallocgc(sizeof *c, nil, 0);
 	c->gobody = fn.data;
 	c->argsize = argsize;
 	c->cleanstack = cleanstack;

src/pkg/runtime/env_plan9.c

@@ -33,7 +33,7 @@ runtime·getenv(int8 *s)
 		runtime·memclr(b, sizeof b);
 		p = b;
 	}else
-		p = runtime·malloc(n+1);
+		p = runtime·mallocgc(n+1, nil, 0);
 	r = runtime·pread(fd, p, n, 0);
 	runtime·close(fd);
 	if(r < 0)

src/pkg/runtime/os_plan9.c

@@ -20,11 +20,11 @@ runtime·mpreinit(M *mp)
 	// Initialize stack and goroutine for note handling.
 	mp->gsignal = runtime·malg(32*1024);
 	mp->gsignal->m = mp;
-	mp->notesig = (int8*)runtime·malloc(ERRMAX*sizeof(int8));
+	mp->notesig = (int8*)runtime·mallocgc(ERRMAX*sizeof(int8), nil, 0);
 
 	// Initialize stack for handling strings from the
 	// errstr system call, as used in package syscall.
-	mp->errstr = (byte*)runtime·malloc(ERRMAX*sizeof(byte));
+	mp->errstr = (byte*)runtime·mallocgc(ERRMAX*sizeof(byte), nil, 0);
 }
 
 // Called to initialize a new m (including the bootstrap m).

src/pkg/runtime/os_windows.c

@@ -143,7 +143,7 @@ runtime·goenvs(void)
 	for(p=env; *p; n++)
 		p += runtime·findnullw(p)+1;
 
-	s = runtime·malloc(n*sizeof s[0]);
+	s = runtime·mallocgc(n*sizeof s[0], nil, 0);
 
 	p = env;
 	for(i=0; i<n; i++) {