[clang][deps] Move injection of -Wno-error from clang-scan-deps to DependencyScanning library
This moves another piece of logic specific to clang-scan-deps into the DependencyScanning library. This makes it easier to check how the original command-line looked like in the library and will enable the library to stop inventing -Wno-error for modular dependencies (see D104036).
Reviewed By: arphaman
Differential Revision: https://reviews.llvm.org/D104031