fix many bugs related to target names being computed inconsistently.
- Centralized computation of a target's file name to a method in
cmTarget. Now that global knowledge is always available the
*_CMAKE_PATH cache variables are no longer needed.
- Centralized computation of link library command lines and link
directory search order.
- Moved computation of link directories needed to link CMake targets
to be after evaluation of linking dependencies.
This also removed alot of duplicate code in which each version had its
own bugs.
This commit is surrounded by the tags
CMake-TargetNameCentralization1-pre
and
CMake-TargetNameCentralization1-post
so make the large set of changes easy to identify.