[libcxx] [test] Include more libraries that normally are linked automatically

As the libcxx tests link with -nostdlib, libraries that normally
are added by default by the compiler driver has to be added
manually.

The "oldnames" library is automatically added when driving linking
with clang-cl. When linking with the plain clang driver, as the
libcxx tests do, the clang driver does the same but only since Clang
12.0). But when linking with -nostdlib, like the libcxx tests do,
the driver defaults aren't added at all, and we need to specify the
defaults manually.

This allows removing a TODO from the Windows CI setup; it turns out
that upgrading to Clang 12.0 didn't help here as expected, sorry about
that mixup.

Differential Revision: https://reviews.llvm.org/D101434