Darwin, libffi, testsuite: Ensure we pick up the convenience lib.

Darwin, libffi, testsuite: Ensure we pick up the convenience lib.

For several Darwin linker versions, the link paths are first traversed
looking for shared libraries, and then again looking for archives.

We want the paths to be searched for both shared and archives in order
so that we will find the non-shared libffi in the testsuite (otherwise
the installed version in the system will be found instead).

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
libffi/ChangeLog:

	* testsuite/lib/libffi.exp: Search for both shared and archive
	in each path in turn.