Fix rewrite of reserved library name in case of -nodefaultlibs

The Driver only checked if nostdlib was set when deciding to add
reserved_lib_stdcxx, but as nostdlib is always exactly nodefaultlibs and
nostartfiles we should be checking one (clearly nodefaultlibs in the
case) as well. This appears to be the only such instance of this in the
codebase.

Differential Revision: http://reviews.llvm.org/D14935

llvm-svn: 253990