- Implement the %args% substitution

- Implement the %args% substitution
- Implement parsing of the .output={bytecode|assembly} item.
- Drop parsing support for translator.optimizes, translator.groks_dash_O,
  optimizer.groks_dash_O, translator.output_is_asm, optimizer.output_is_asm
- Add parsing support for translator.output and optimizer.output
- Add optimizer.required parsing support
- Add linker.libs and linker.libpaths parsing support
- Fix error messages to list correct set of tokens expected.
- Rename FileReadable -> FileIsReadable (changed in CompilerDriver.cpp)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@16023 91177308-0d34-0410-b5e6-96231b3b80d8