compiler: implement unsafe.Alignof and unsafe.Sizeof for generic code

For some reason, these aren't lowered when a generic function is
instantiated by the SSA package.

I've left unsafe.Offsetof to be implemented later, it's a bit difficult
to do correctly the way the code is currently structured.

compiler/testdata/generics.go

@@ -1,5 +1,7 @@
 package main
 
+import "unsafe"
+
 type Coord interface {
 	int | float32
 }
@@ -9,6 +11,8 @@ type Point[T Coord] struct {
 }
 
 func Add[T Coord](a, b Point[T]) Point[T] {
+	checkSize(unsafe.Alignof(a))
+	checkSize(unsafe.Sizeof(a))
 	return Point[T]{
 		X: a.X + b.X,
 		Y: a.Y + b.Y,
@@ -22,3 +26,5 @@ func main() {
 	var ai, bi Point[int]
 	Add(ai, bi)
 }
+
+func checkSize(uintptr)