With PushScope and PopScope, keeping track of another bit of data for
each scope isn't easy. Instead, store it as another CMake variable so it
gets implicitly tracked along with everything else.
This works in a revert of commit
7d674b5f0b28a610333644d417c2e8cb796cc9e4.
This reverts commit v3.1.0-rc1~557^2~2 (ClearMatches: Only clear matches
which were actually set, 2014-03-12). The optimization did not track
the match count in the same scope as the variables, allowing possible
inconsistency.
Resolve conflicts in Source/cmIfCommand.cxx, Source/cmMakefile.cxx,
and Source/cmMakefile.h by moving the changes to the new location
of the code involved.
