Add external includes as SYSTEM

For instance, this disables warnings generated in third party headers (such as numerous -Wzero-as-null-pointer-constant in vorbisfile.h)

Author: AMDmi3

CMakeLists.txt

@@ -38,15 +38,15 @@ ENDIF(LINUX)
 SET(CMAKE_MODULE_PATH ${PROJECT_SOURCE_DIR}/share/cmake)
 FIND_PACKAGE(SDL2 REQUIRED)
 IF(SDL2_FOUND)
-	INCLUDE_DIRECTORIES(${SDL2_INCLUDE_DIR})
+	INCLUDE_DIRECTORIES(SYSTEM ${SDL2_INCLUDE_DIR})
 	SET(ALL_LIBRARIES ${ALL_LIBRARIES} ${SDL2_LIBRARY})
 ELSE(SDL2_FOUND)
 	MESSAGE(FATAL_ERROR "libSDL2 not found")
 ENDIF(SDL2_FOUND)
 
 FIND_PACKAGE(OpenGL REQUIRED)
 IF(OPENGL_FOUND)
-	INCLUDE_DIRECTORIES(${OPENGL_INCLUDE_DIR})
+	INCLUDE_DIRECTORIES(SYSTEM ${OPENGL_INCLUDE_DIR})
 	SET(ALL_LIBRARIES ${ALL_LIBRARIES} ${OPENGL_LIBRARIES})
 ELSE(OPENGL_FOUND)
 	MESSAGE(FATAL_ERROR "OpenGL not found")
@@ -73,7 +73,7 @@ FIND_PATH(ALUT_INCLUDE_DIR alut.h
 	PATH_SUFFIXES include/AL include)
 IF(ALUT_INCLUDE_DIR)
 	MESSAGE(STATUS "Found alut headers: ${ALUT_INCLUDE_DIR}")
-	INCLUDE_DIRECTORIES(${ALUT_INCLUDE_DIR})
+	INCLUDE_DIRECTORIES(SYSTEM ${ALUT_INCLUDE_DIR})
 ELSE(ALUT_INCLUDE_DIR)
 	MESSAGE(FATAL_ERROR "alut headers not found")
 ENDIF(ALUT_INCLUDE_DIR)
@@ -96,7 +96,7 @@ FIND_PATH(OGG_INCLUDE_DIR ogg/ogg.h
 	PATH_SUFFIXES include)
 IF(OGG_INCLUDE_DIR)
 	MESSAGE(STATUS "Found ogg headers: ${OGG_INCLUDE_DIR}")
-	INCLUDE_DIRECTORIES(${OGG_INCLUDE_DIR})
+	INCLUDE_DIRECTORIES(SYSTEM ${OGG_INCLUDE_DIR})
 ELSE(OGG_INCLUDE_DIR)
 	MESSAGE(FATAL_ERROR "ogg headers not found")
 ENDIF(OGG_INCLUDE_DIR)
@@ -132,7 +132,7 @@ FIND_PATH(VORBISFILE_INCLUDE_DIR vorbis/vorbisfile.h
 	PATH_SUFFIXES vorbis include)
 IF(VORBISFILE_INCLUDE_DIR)
 	MESSAGE(STATUS "Found vorbisfile headers: ${VORBISFILE_INCLUDE_DIR}")
-	INCLUDE_DIRECTORIES(${VORBISFILE_INCLUDE_DIR})
+	INCLUDE_DIRECTORIES(SYSTEM ${VORBISFILE_INCLUDE_DIR})
 ELSE(VORBISFILE_INCLUDE_DIR)
 	MESSAGE(FATAL_ERROR "vorbisfile headers not found")
 ENDIF(VORBISFILE_INCLUDE_DIR)
@@ -154,7 +154,7 @@ FIND_PATH(FREETYPE_INCLUDE_DIR_freetype2 freetype/config/ftheader.h
 	PATH_SUFFIXES freetype2)
 IF(FREETYPE_INCLUDE_DIR_freetype2)
 	MESSAGE(STATUS "Found freetype2 headers: ${FREETYPE_INCLUDE_DIR_freetype2}")
-	INCLUDE_DIRECTORIES(${FREETYPE_INCLUDE_DIR_freetype2})
+	INCLUDE_DIRECTORIES(SYSTEM ${FREETYPE_INCLUDE_DIR_freetype2})
 ELSE(FREETYPE_INCLUDE_DIR_freetype2)
 	EXEC_PROGRAM("freetype-config" ARGS "--cflags" OUTPUT_VARIABLE freetype2_CFLAGS)
 	IF(freetype2_CFLAGS)