This change allows the swift driver to link the ubsan runtime if
`-sanitize=undefined` is specified.
This is useful for sanitizing linked Objective-C code.
Similarly to Clang, the flag enables coverage instrumentation, and links
`libLLVMFuzzer.a` to the produced binary.
Additionally, this change affects the driver logic, and enables the
concurrent usage of multiple sanitizers.
- Added missing ifdef guard in PointerIntEnum header
- Consistent naming convention for ifdef guards
- Consistent 'end namespace swift'
- Consistent single EOL at end of header files