Don't compute optimized PointerKind for unoptimized builds

This saves us both the Freeze/Unpin queries, and avoids placing
noalias attributes, which have a compile-time impact on LLVM
even in optnone builds (due to always_inline functions).

src/test/codegen/function-arguments.rs

@@ -1,4 +1,4 @@
-// compile-flags: -C no-prepopulate-passes
+// compile-flags: -O -C no-prepopulate-passes
 // ignore-tidy-linelength
 // min-system-llvm-version: 12.0