This relands #165277 by reverting #169397.
This also relands the corresponding Bazel port by reverting #169410.
The original revert was due to a report of a broken build, which was
later resolved by fully clearing the build directory.
This removes the dependency on clangDriver from clangFrontend and
flangFrontend.
This refactoring is part of a broader effort to support driver-managed
builds for compilations using C++ named modules and/or Clang modules.
It is required for linking the dependency scanning tooling against the
driver without introducing cyclic dependencies, which would otherwise
cause build failures when dynamic linking is enabled.
In particular, clangFrontend must no longer depend on clangDriver
for this to be possible.
This change was discussed in the following RFC:
https://discourse.llvm.org/t/rfc-new-clangoptions-library-remove-dependency-on-clangdriver-from-clangfrontend-and-flangfrontend/88773
