libgcc, Darwin: No early install for the compatibility libgcc_s.1.dylib.

libgcc, Darwin: No early install for the compatibility libgcc_s.1.dylib.

On Darwin, GCC now uses a libgcc_s.1.1 for builtins and forwards the system
unwinder.  We do, however, build a backwards compatibility libgcc_s.1.dylib.
However, this is not needed by GCC and can cause incorrect operation when
DYLD_LIBRARY_PATH is in use.

Since we do not need or use it during the build, the solution is to skip the
installation into the $build/gcc directory.

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

	* config/t-slibgcc-darwin (install-darwin-libgcc-stubs): Skip the
	install of libgcc_s.1.dylib when the installation is into the build
	gcc directory.

(cherry picked from commit 163f0f2267370575a9950e7e30a2c9cd72f559f0)