[Driver] Let -gline-tables-only win when it comes after -gmodules.

The -gmodules option is all about putting debug type info into clang
modules and for line tables the type information is irrelevant, so
combining these two options makes no sense.
This commmit fixes the behavior to match the one  documented on the
clang man page: the last -g... option wins.

<rdar://problem/27059770>

llvm-svn: 283810