Add an ability to replace some source files before building.

CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.9)
+cmake_minimum_required(VERSION 3.20)
 
 set(CMAKE_CONFIGURATION_TYPES Debug Release CACHE STRING INTERNAL FORCE)
 
@@ -35,6 +35,11 @@ if (MSVC)
     patch_file(${WEBRTC_SOURCE_DIR}/build/config/win/BUILD.gn ":static_crt" ":dynamic_crt")
 endif ()
 
+# Copy all files from 'patches' directory to 'webrtc/src'
+# For example, 'patches/api/foo.h' will be copied to 'webrtc/src/api/foo.h'
+include(PatchSources)
+patch_sources("${CMAKE_CURRENT_SOURCE_DIR}/patches" "${CMAKE_CURRENT_SOURCE_DIR}/webrtc/src")
+
 include(AddWebRTCTarget)
 add_webrtc_target(${WEBRTC_SOURCE_DIR} ${WEBRTC_BUILD_DIR})
 

cmake/PatchSources.cmake

@@ -0,0 +1,10 @@
+function(patch_sources PATCH_DIR SOURCE_DIR)
+	file(GLOB_RECURSE PATCHED_SOURCES RELATIVE ${PATCH_DIR} ${PATCH_DIR}/*)
+	list(REMOVE_ITEM PATCHED_SOURCES ".gitkeep")
+	foreach (file ${PATCHED_SOURCES})
+		message(STATUS "Patching ${file}...")
+		set(destination "${SOURCE_DIR}/${file}")
+		cmake_path(GET destination PARENT_PATH dest_dir)
+		file(COPY ${PATCH_DIR}/${file} DESTINATION ${dest_dir})
+	endforeach ()
+endfunction()