This also fixes a missing header in the SDK that rtags needs to work
properly. The underlying cause is that C++ headers got shuffled around a
lot in libc++ 3.8 (I believe) and became more standards-compliant, which
led to a lot of C-compatible passthrough header files being added to it
like math.h, which defines some C++-compatible versions of standard
functions like signbit, while #include_next'ing the system math.h. In
this case, including the SDK was stuffing another math.h in front of the
libc++ shim, which led to all sorts of mysterious failures.
Adds dependency to MacOS_SDK 10.9 and accordingly to the macosx
deployment target to configure SDK-based deployment in rtags. In detail,
rtags makes use of launch_activate_socket() which is available in
launchd.h >10.9. Latter is still not available through
apple-opensource-releases, if ever. Thus, the deployment target and
build input have to be added to let rtags build scripts make use of MAC_OS_X_VERSION_MAX_ALLOWED correctly.