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_conservative.go

@@ -263,7 +263,7 @@ func calculateHeapAddresses() {
 // alloc tries to find some free space on the heap, possibly doing a garbage
 // collection cycle if needed. If no space is free, it panics.
 //go:noinline
-func alloc(size uintptr) unsafe.Pointer {
+func alloc(size uintptr, layout unsafe.Pointer) unsafe.Pointer {
 	if size == 0 {
 		return unsafe.Pointer(&zeroSizedAlloc)
 	}