Document CMAKE_<LANG>_FLAGS variable (#14305)

We already document the variables CMAKE_<LANG>_FLAGS_{DEBUG, MINSIZEREL,
RELEASE, RELWITHDEBINFO}. However, CMAKE_<LANG>_FLAGS is not documented,
even though it's available (and useful).
target_link_libraries: Add PUBLIC/PRIVATE/INTERFACE keyword signature

Add a new signature to help populate INTERFACE_LINK_LIBRARIES and
LINK_LIBRARIES cleanly in a single call.  Add policy CMP0023 to control
whether the keyword signatures can be mixed with uses of the plain
signatures on the same target.
FindQt4: Re-add QAxServer to the QT_MODULES.

This was removed instead of moved in commit b8af46cb (FindQt4: Don't
fail if certain Qt modules are unavailable.).
Test COMPILE_DEFINITIONS target property get/set/get round-trip

Teach the Preprocess test to get, set, and then get the same value for
the COMPILE_DEFINITIONS target property and verify that the value is not
changed.  This ensures the internal structured storage of the property
value can reproduce the original string value.
CMake Nightly Date Stamp
Merge topic 'doc-CMAKE_lang_FLAGS'

41bb95f Document CMAKE_<LANG>_FLAGS variable (#14305)
Merge topic 'fix-FindQt4-available-modules'

d57c1c1 FindQt4: Re-add QAxServer to the QT_MODULES.
Merge topic 'compile-defs-debugging'

a43e5e0 Test COMPILE_DEFINITIONS target property get/set/get round-trip
Merge topic 'tll-new-signatures'

b655865 target_link_libraries: Add PUBLIC/PRIVATE/INTERFACE keyword signature
Tests/RunCMake: Document stripping of expected output

Document that trailing newlines are stripped from the -stdout.txt
and -stderr.txt content before using as a regular expression.
export: Error when exporting a target without a language

First, it prevents a NULL dereference and second it reiterates that
targets without languages are not supported by CMake.

Add a RunCMake.ExportWithoutLanguage test exporting a library without a
languages.
Merge topic 'doc-RunCMake-strips-expected'

c80a4f9 Tests/RunCMake: Document stripping of expected output
Merge topic 'dev/export-target-without-language'

5837f19 export: Error when exporting a target without a language