llvm-rc: Write dep files to binary tree
Moved the dependency file creation flags to the CMAKE_DEPFILE_FLAGS_RC for llvm-rc and use the place holder.
Additionally a correction to the preprocessor selection was added to select the preprocessor for an active language and not just because a compiler was set.
Tests were conducted manually to
- validate the dependency file creation outside of the source tree
- verify the dependencies are picked up by the make tool used.
Fixes: #20493 (closed)
Backport: release
Topic-rename: llvm-rc-depfile
Edited by Brad King