Make pkg-config regress tests pass:

Make pkg-config regress tests pass:
- Allow to override PKG_CONFIG and check correct place in logfile.
- Replace "if ...; then false; fi" with a simple ! .
- Remove comments about failing test which do not fail.
- Adapt regress to changes in pkg-config rev 1.64 and 1.72 regarding
  static and missing tests.
OK jasper@