Don't include LDFLAGS in `wx-config --libs` output.

Don't include LDFLAGS in `wx-config --libs` output.

Use a separate WXCONFIG_LDFLAGS variable for the flags which should be used
when linking applications using wxWidgets and not wxWidgets itself.

The only intentional effect this change is supposed to have right now is that
-arch options added to LDFLAGS when building wx for multiple architectures
under OS X are not used for building the applications any more.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@62459 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775