stage2: rework a lot of stuff

AstGen:
 * rename the known_has_bits flag to known_non_opv to make it better
   reflect what it actually means.
 * add a known_comptime_only flag.
 * make the flags take advantage of identifiers of primitives and the
   fact that zig has no shadowing.
 * correct the known_non_opv flag for function bodies.

Sema:
 * Rename `hasCodeGenBits` to `hasRuntimeBits` to better reflect what it
   does.
   - This function got a bit more complicated in this commit because of
     the duality of function bodies: on one hand they have runtime bits,
     but on the other hand they require being comptime known.
 * WipAnonDecl now takes a LazySrcDecl parameter and performs the type
   resolutions that it needs during finish().
 * Implement comptime `@ptrToInt`.

Codegen:
 * Improved handling of lowering decl_ref; make it work for
   comptime-known ptr-to-int values.
   - This same change had to be made many different times; perhaps we
     should look into merging the implementations of `genTypedValue`
     across x86, arm, aarch64, and riscv.

src/codegen.zig

@@ -377,7 +377,7 @@ pub fn generateSymbol(
             const field_vals = typed_value.val.castTag(.@"struct").?.data;
             for (field_vals) |field_val, index| {
                 const field_ty = typed_value.ty.structFieldType(index);
-                if (!field_ty.hasCodeGenBits()) continue;
+                if (!field_ty.hasRuntimeBits()) continue;
                 switch (try generateSymbol(bin_file, src_loc, .{
                     .ty = field_ty,
                     .val = field_val,