Fix OpenSSL detection when an explicit path is given

Fix OpenSSL detection when an explicit path is given

The previous OpenSSL detection was skipping the library checks when an
explicit path was presented. Resulting in no -lssl flag being passed to
the linker.

Rational for this fix:
 pkg-config presents location-neutral details.

 The explicit checks are likewise neutral provided the LIBS environment
  variable has been set with the explicit path.

 User presented path must be used regardless of which the library checks
  are used in detection.

So...

 Always perform the checks with optionally set LIBS and keep the
 user provided path explicitly separate from the pkg-config *_LIBS
 variable. Only assemble the parts into SSLLIB once all have been
 identified.