Move functionality of UniversalDriver to the entry point file.

Move functionality of UniversalDriver to the entry point file.

UniversalDriver was used as a dispatcher to each platform-specific driver.
It had its own Options.td file. It was not just too much to parse only a
few options (we only want to parse -core, -flavor or argv[0]),
but also interpreted arguments too early. For example, if you invoke lld as
"lld -flavor gnu ... -help", then you'd get the UniversalDriver's help
message instead of GnuDriver's. This patch eliminates the use of Options
from the dispatcher.

http://reviews.llvm.org/D17686

llvm-svn: 262190