Revert svn r176894 and r177658.

Changing -ccc-install-dir to affect cc1's resource-dir setting broke our
internal LNT tests. After discussing the situation with Jim, we've decided to
pursue an alternate approach. We really want the resource-dir to be located
relative to clang, even when using -ccc-install-dir, but we're going to
add a fallback setting for the libc++ headers if they don't exist alongside
the compiler.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@177815 91177308-0d34-0410-b5e6-96231b3b80d8