Merge topic 'makefiles-compiler-deps-optims'

2c71d051fa Makefiles Generators: use compiler for dependencies generation
afd0f6785d Refactoring: Abstract Makefile line continuation format
b6068ce407 Refactoring: enhance include file filtering
3401403f69 Refactoring: Introduce place-holder for dependency target.
a97c41bf8b Refactoring: Makefiles Generators: Add support for various depends scanners

Acked-by: Kitware Robot <kwrobot@kitware.com>
Acked-by: Brad King <brad.king@kitware.com>
Merge-request: !5528

Help/manual/cmake-variables.7.rst

@@ -387,6 +387,7 @@ Variables that Control the Build
    /variable/CMAKE_DEFAULT_BUILD_TYPE
    /variable/CMAKE_DEFAULT_CONFIGS
    /variable/CMAKE_DISABLE_PRECOMPILE_HEADERS
+   /variable/CMAKE_DEPENDS_USE_COMPILER
    /variable/CMAKE_ENABLE_EXPORTS
    /variable/CMAKE_EXE_LINKER_FLAGS
    /variable/CMAKE_EXE_LINKER_FLAGS_CONFIG

Help/release/dev/makefiles-dependencies-use-compiler.rst

@@ -0,0 +1,5 @@
+makefiles-dependencies-use-compiler
+-----------------------------------
+
+* The :ref:`Makefile Generators` gained the capability, for a selection of
+  compilers, to use the compiler itself to generate implicit dependencies.

Help/variable/CMAKE_DEPENDS_USE_COMPILER.rst

@@ -0,0 +1,9 @@
+CMAKE_DEPENDS_USE_COMPILER
+--------------------------
+
+.. versionadded:: 3.20
+
+For the :ref:`Makefile Generators`, source dependencies are now, for a
+selection of compilers, generated by the compiler itself. By defining this
+variable with value ``FALSE``, you can restore the legacy behavior (i.e. using
+``CMake`` for dependencies discovery).