[libc++] [test] Fix `__has_include` usage, expand condvarany and spaceship coverage (#94120)

Three unrelated, small improvements:

* `test_macros.h` was incorrectly saying `__has_include("<version>")`
instead of `__has_include(<version>)`.
+ This caused `<ciso646>` to always be included (noticed because MSVC's
STL emitted a deprecation warning).
  + I searched all of LLVM and found no other occurrences.
* `thread.condition.condvarany/wait_for_pred.pass.cpp` forgot to test
anything.
  + I followed what `wait_for.pass.cpp` is testing.
* Uncomment spaceship test coverage.