When configured files are modified we should regenerate them.

Currently when a configured file is removed from the build directory,
running the build command will not regenerate the file. Now detect
this and will rerun cmake properly when a user issues the build
command.
Update the ninja generator to track configured files.

Unlike the Makefile generator the ninja generator did not tack any of
its output files, so if they changed the generator would not rerun.
Merge topic 'add-try_compile-options' into 13582_configured_file_regeneration

Conflicts:
	Source/cmCoreTryCompile.cxx
Merge topic '13582_configured_file_regeneration' into next

bd1eb6b Merge topic 'add-try_compile-options' into 13582_configured_file_regeneration
4f09d96 Update the ninja generator to track configured files.
21bf95d When configured files are modified we should regenerate them.