Fix Mac OS X architecture detection for non-default Xcode setup.

Fix Mac OS X architecture detection for non-default Xcode setup.

The arch.test script is now using SDK settings passed to it.
If you install Xcode without the "UNIX Development" option, this
is essential to let the compiler find standard headers and let
the test program compile successfully.

In addition, let configure pass the SDK settings given on the
command line to the arch.test script.

Change-Id: I49601d3068d83a71e21fdbac287857f2b7abedd1
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>