Always use dlopen and dlsym to load libsolv

Previous implementation used weak symbols on all platforms except Haiku. Mac OS X also does not support this use of weak symbols. In the discussion of #10028 it was decided that probably more platforms will have problems with this approach, so instead use the approach that always works.
Add HOST_LIBSUPC++ to fix compilation on MacOS X
Determine how to invoke sed with extended regexp

This will require re-running configure
libroot_build: fs_darwin: fdopendir(): close FD on success

fdopendir() is supposed to consume the specified FD on success.