What is the Fedora equivalent to the Debian/Ubuntu package search pages?

The Fedora package search application is available at: http://apps.fedoraproject.org/packages

I use http://koji.fedoraproject.org

I hadn't seen PkgDB before, so I can't say much about it. Koji works well but the only caveat is that it shows packages that have been built and they aren't necessarily in the repository yet.

The Fedora PkgDB does have a search syntax so you could search for builds with /usr/bin/g++ in it by searching for file:/usr/bin/g++ and click Builds. Click on the blue (i) for more details. The GCC package has several sub-packages, as described in the gcc.spec file you showed above, which has added to the confusion.