[clang] [clang-cl] Allow a colon after /Fo option (PR #87209)

[Reid Kleckner via cfe-commits]

rnk wrote:

That's interesting! I wonder how long the /F flags have accepted trailing colons. That form seems a lot more readable.

I went looking for examples of how to do this with fewer aliases, but it looks like this is what is done currently:
https://github.com/llvm/llvm-project/blob/main/clang/include/clang/Driver/Options.td#L5650

The only other prior art I could identify was the JoinedOrSeparate kind, which we could generalize to "JoinedOrEq" or "JoinedOrColon" in tablegen, and that would be the most maintainable, most general fix I can think of.

Regardless, I'm happy to approve this and other future patches to add the aliases in the meantime.

https://github.com/llvm/llvm-project/pull/87209