Bug#18187290 ISSUE WITH BUILDING MYSQL USING CMAKE 2.8.12

We want to upgrade to VS2013 on Windows.
In order to do this, we need to upgrade to cmake 2.8.12
This has introduced some incompatibilities for .pdb files,
and "make install" no longer works.

To reproduce:
  cmake --build . --target package --config debug

The fix:
Rather than installing .pdb files for static libraries, we use the /Z7 flag
to store symbolic debugging information in the .obj files.