runtime: use new instead of newobject to create hmap in makemap

The runtime.hmap type is known at compile time.
Using new(hmap) avoids loading the hmap type from the maptype
supplied as an argument to makemap which is only known at runtime.

This change makes makemap consistent with makemap_small
by using new(hmap) instead of newobject in both functions.

Change-Id: Ia47acfda527e8a71d15a1a7a4c2b54fb923515eb
Reviewed-on: https://go-review.googlesource.com/91775
Run-TryBot: Martin Möhrmann <moehrmann@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

src/runtime/hashmap.go

@@ -309,7 +309,7 @@ func makemap(t *maptype, hint int, h *hmap) *hmap {
 
 	// initialize Hmap
 	if h == nil {
-		h = (*hmap)(newobject(t.hmap))
+		h = new(hmap)
 	}
 	h.hash0 = fastrand()