Quote some more destination paths with variables

Just defensive CMake-ing. I pulled this from D115544 and D99484 which
are blocked on some lldb CI failures I don't yet understand. Hoping to land
something smaller in the meantime.

Reviewed By: #libc, ldionne

Differential Revision: https://reviews.llvm.org/D115566

GitOrigin-RevId: ddcc02dbcc4767b289776f73f26fe444964d0942
1 file changed