Add KDEClangFormat cmake support

Summary:
This allows devs to run: "make clang-format" and format all files easily
using the preset KDE clang format style

This patch adds support so devs can easily test the intended formatting
now, it doesn't change the code yet.

Doing an initial run to commit everything will happen later.

Test Plan:
Ran script
git diff was full of amazingly cleaned code

See D25134

CMakeLists.txt

@@ -14,6 +14,7 @@ find_package(ECM 5.38 REQUIRED NO_MODULE)
 include(FeatureSummary)
 include(WriteBasicConfigVersionFile)
 include(GenerateExportHeader)
+include(KDEClangFormat)
 
 # where to look first for cmake modules, before ${CMAKE_ROOT}/Modules/ is checked
 set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} ${ECM_MODULE_PATH} ${ECM_KDE_MODULE_DIR})
@@ -739,6 +740,10 @@ endif()
 
 add_subdirectory(kconf_update)
 
+# add clang-format target for all our real source files
+file(GLOB_RECURSE ALL_CLANG_FORMAT_SOURCE_FILES *.cpp *.h)
+kde_clang_format(${ALL_CLANG_FORMAT_SOURCE_FILES})
+
 feature_summary(WHAT ALL INCLUDE_QUIET_PACKAGES FATAL_ON_MISSING_REQUIRED_PACKAGES)
 
 include(CMakePackageConfigHelpers)