By default, the linker in use under OpenBSD is the linker of base, which
don't include /usr/local/lib where libstdc++ of gcc-4.9 lives. We need
to add this directory to linker-path-search (using -L).
Search the path of libstdc++.a, which is a known name (libstdc++.so has
SO_VERSION) in the same directory.
049d76bdd2