Hardlinking to a symlink is not permitted, so use "swift-frontend"
instead of "swift" as the hard-link target.
Also, update one Linux-specific test to check for swift-frontend.
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
