[llvm] [llvm] Fix cmake string expansion in CrossCompile.cmake (PR #138901)

[David Truby via llvm-commits]

DavidTruby wrote:

I completely forgot that I'd submitted this as I've been really busy with other things...
I don't have the time to update all the places where this needs doing and test it all; would people be ok with submitting this as-is for now so we can remove the special cases for ccache+Windows, and punting the issue of fixing it all into a future patch?

https://github.com/llvm/llvm-project/pull/138901