…is being used.Unless cross-module-optimization is disabled (which we don't really support at this time), the driver in this case will create a single frontend invocation that emits both the module and performs codegen.Cherry-pick of upstream:29f0ec2

…ty string instead of the full list of object files.This reduces unnecessary processing for huge modules with hundreds of source files.Cherry-pick:c413bd3

…p specific mnemonics.

…mization modes interact as we expect.The tests highlight a couple cases that are currently known to be wrong so we can fix and test them without just manually building all possible combinations.Chery-pick:f6302a2

Explicitly disable cross-module optimization in `exec` configs so that Swift tools can be built in parallel to speed up critical build paths.Cherry-pic:d1ecc8a

Signed-off-by: Brentley Jones <github@brentleyjones.com>

…llel compilation.In the future, we should consider whether we should more strictly control where these flags can be applied, since they don't just control optimizations but also how the driver plans its work.Cherry-pick:ab55a12

…sed and `-wmo` is passed on the command line.Cherry-pick:66a6a6b