runtime: make Go and C mallocgc signatures match

Previously, the flags argument to mallocgc was an int in Go,
but a uint32 in C.  Change the Go type to use uint32 so these
agree.  The largest flag value is 2 (and of course no flag
values are negative), so this won't change anything on little
endian architectures, but it matters on big endian.

LGTM=rsc
R=khr, rsc
CC=golang-codereviews
https://golang.org/cl/169920043

src/runtime/malloc.go

@@ -43,7 +43,7 @@ var zerobase uintptr
 // Allocate an object of size bytes.
 // Small objects are allocated from the per-P cache's free lists.
 // Large objects (> 32 kB) are allocated straight from the heap.
-func mallocgc(size uintptr, typ *_type, flags int) unsafe.Pointer {
+func mallocgc(size uintptr, typ *_type, flags uint32) unsafe.Pointer {
 	if size == 0 {
 		return unsafe.Pointer(&zerobase)
 	}
@@ -346,7 +346,7 @@ marked:
 
 // implementation of new builtin
 func newobject(typ *_type) unsafe.Pointer {
-	flags := 0
+	flags := uint32(0)
 	if typ.kind&kindNoPointers != 0 {
 		flags |= flagNoScan
 	}
@@ -355,7 +355,7 @@ func newobject(typ *_type) unsafe.Pointer {
 
 // implementation of make builtin for slices
 func newarray(typ *_type, n uintptr) unsafe.Pointer {
-	flags := 0
+	flags := uint32(0)
 	if typ.kind&kindNoPointers != 0 {
 		flags |= flagNoScan
 	}