Use `clang` rather than `clang++` as the linker driver. This ensures
that we do not force a C++ runtime on the general code. This is fine
for now as C++ interop is not yet available for Swift. This prevents
the accidental mix-and-match of various C++ runtimes. This can cause
problems on platforms like android where `libstdc++` is an unsupported
runtime but is generally the default for Linux platforms.
inside a swift ast section in an object file so it can be passed to the
linker. The driver automatically wraps merged swiftmodules iff the target
is ELF.
rdar://problem/22407666
Swift SVN r31641
