This option is useful for clang and clang-cl.
To expose to clang-cl, can we just make the original option a CoreOption instead of adding an alias of the same name here?
This breaks tests on macOS: http://126.96.36.199/macm1/53215/step_7.txt
Please take a look and revert for now if it takes a while to fix.
@thakis I reverted it. The fast value of the option doesn't seem to be working for clang-cl on Mac!