Normalize full paths in implicit link library list

Teach CMakeParseImplicitLinkInfo to convert implicit link library full
paths to a canonical form.  This makes them more reproducible in case
different language compiler front-ends add the same library by different
paths e.g. ".../libA.a" and "...//libA.a".

Add a case to the CMake.ImplicitLinkInfo test to cover removal of extra
slashes from both library and directory paths.
Merge topic 'implicit-lib-canonical-path' into next

10e8b2d Normalize full paths in implicit link library list