Patch to support -nodefaultlibs flag on Linux targets (fixes llvm bug 11172)

Hi,

I was experimenting with getting libc++abi and libc++ working on
Linux, and I noticed that mainline clang doesn't honor the
-nodefaultlibs flag on that platform. There is an open bug for this
issue: http://llvm.org/bugs/show_bug.cgi?id=11172. I've attached a
patch to tools/Driver.cpp that is my best guess at a fix, based on how
-nodefaultlibs is handled for other platforms in that file. The patch
also adds a new test for the feature, derived from the -nostdlib flag
test.

Thanks,
Andrew

linux.nodefaultlibs.patch (2.23 KB)

Thanks, committed in r156771! =]