compiler, runtime: add layout parameter to runtime.alloc

This layout parameter is currently always nil and ignored, but will
eventually contain a pointer to a memory layout.

This commit also adds module verification to the transform tests, as I
found out that it didn't (and therefore didn't initially catch all
bugs).

src/runtime/gc_leaking.go

@@ -13,7 +13,7 @@ import (
 // Ever-incrementing pointer: no memory is freed.
 var heapptr = heapStart
 
-func alloc(size uintptr) unsafe.Pointer {
+func alloc(size uintptr, layout unsafe.Pointer) unsafe.Pointer {
 	// TODO: this can be optimized by not casting between pointers and ints so
 	// much. And by using platform-native data types (e.g. *uint8 for 8-bit
 	// systems).