Add support for codelite IDE project fles
Tests: Fix find-package mode test.

The all target was depending on the clean and pngtest targets, but
when running the tests with -jN, those can be executed out of order.

Make the main.o target depend on the clean target instead to fix
this.
AddDependencies: new policy requires dependencies to exist

Added new policy CMP0046 which requires dependencies added by
add_dependencies() to actually exist.
cmComputeLinkDepends: Hold a const global generator.
cmGeneratorTarget: Hold a const global generator.
cmGlobalGenerator: Make some API const.
cmGlobalGenerator: Make CheckALLOW_DUPLICATE_CUSTOM_TARGETS const
cmGlobalGenerator: Make SelectMakeProgram const.
cmake: Future-proof --find-package mode.

Create cmGeneratorTargets before generating generate-time information.
C++ interfaces for querying build information is increasingly only
available at generate time through the cmGeneratorTarget class.  Ensure
that the required cmGeneratorTarget instances are created.  Use the
cmGlobalGenerator access API to access the relevant cmGeneratorTarget
instead of creating a temporary one on the stack.
Merge topic 'fix-FindPackageModeMakefileTest-Makefile'

dea71aae Tests: Fix find-package mode test.
Merge topic 'fix-find-package-mode'

a7f393dc cmake: Future-proof --find-package mode.
Merge topic 'constify'

2cbf0311 cmGlobalGenerator: Make SelectMakeProgram const.
b4ff38a5 cmGlobalGenerator: Make CheckALLOW_DUPLICATE_CUSTOM_TARGETS const
8aeddf1f cmGlobalGenerator: Make some API const.
8fd0f2a7 cmGeneratorTarget: Hold a const global generator.
46315320 cmComputeLinkDepends: Hold a const global generator.
Merge topic 'missing-dependency-error'

0bf6f13b AddDependencies: new policy requires dependencies to exist
Merge topic 'support-codelite-ide-generator'

0c4e8c70 Add support for codelite IDE project fles