This is step 2 towards fixing #77548.
In the codegen and codegen-units test suites, the `//` comment markers
were kept in order not to affect any source locations. This is because
these tests cannot be automatically `--bless`ed.
LLVM 10 includes a009a60a917bc30940422bcef73f8270566d78db which will
print value numbers for unnamed func args.
Update these tests to be in line with the referenced clang tests.
