Reland 198fbcb8, "Driver: Don't look for libc++ headers in the install...

Reland 198fbcb8, "Driver: Don't look for libc++ headers in the install directory on Android.", which was reverted in b3249027.

Fixed the test case to set --sysroot, which lets it succeed in the case where
a directory named "/usr/include/c++/v1" or "/usr/local/include/c++/v1" exists.

Original commit message:
> The NDK uses a separate set of libc++ headers in the sysroot. Any headers
> in the installation directory are not going to work on Android, not least
> because they use a different name for the inline namespace (std::__1 instead
> of std::__ndk1).
>
> This effectively makes it impossible to produce a single toolchain that is
> capable of targeting both Android and another platform that expects libc++
> headers to be installed in the installation directory, such as Mac.
>
> In order to allow this scenario to work, stop looking for headers in the
> install directory on Android.

Differential Revision: https://reviews.llvm.org/D71154