Improve support for -g options accepted by Clang:

1. Accept flags -g[0-3], -ggdb[0-3], -gdwarf-[2-4] and collapse them to simple -g (except -g0/-ggdb0).
2. Produce driver error on unsupported formats (-gcoff, -gstabs, -gvms) and options (-gtoggle).
3. Recognize and ignore flags -g[no-]strict-dwarf, -g[no-]record-gcc-switches.

llvm-svn: 158906