Mac builds require that Qt be built from sources since the binary Qt
package is built against the clang libstdc++ C++ support library and
we need it built against the more modern libc++ C++ support library.
git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@4963 ab8295b8-cf94-4d9e-aec4-7959e3be5d79