When enabling the early swift driver on Windows, these tests need to be
adjusted for the new driver name that is reported. Add an additional
spelling for the driver to accommodate that for the testsuite.
Build swift-frontend as the primary Swift binary, and have
swift/swiftc/etc. symlink over to it. This is a step toward allowing
swift-driver to replace the swift and swiftc binaries.
Clang 8 or 9 seems to have changed from EXE to exe. Allow both
capitalizations (which is not important in Windows) as a workaround.
Maybe in the future we can remove the uppercase option.
- Outlaw duplicate input files, fix driver, fix tests, and add test.
- Reflect that no buffer is present without a (possibly pseudo) named file.
- Reflect fact that every input has a (possible pseudo) name.
- Break up CompilerInstance::setup.
Don't bail on dups.
