Static libraries don't have PDB files. A PDB that would previously end
up installed alongside a static library belonged in fact to the dynamic
version of the same library built at the same time.
This was because the former minstall.Installer implementation, when
installing a file target, also blindly copied any *.pdb file it found
whose filename was matching the target. So, for example installing
foo.dll and foo.a would also install two copies of foo.pdb into both
bin/ and lib/, which doesn't seem like the right thing to do - foo.pdb
should only get installed with foo.dll.