BUILD: prefer pkg-config for freetype2 detection

This can solve numerous problems such as:
http://www.cmake.org/Bug/view.php?id=13959
http://www.cmake.org/Bug/view.php?id=14601

If pkg-config or freetype2.pc is not found, then fall back to the
FindFreetype.cmake module logic.

Restrict to UNIX since I only tested it here.

src/cguittfont/CMakeLists.txt

@@ -1,17 +1,29 @@
-include_directories(
-  ${IRRLICHT_INCLUDE_DIR}
-  ${FREETYPE_INCLUDE_DIRS}
-)
-
 # CGUITTFont authors, y u no include headers you use?
 #   Do not add CGUITTFont.cpp to the line below.
 #   xCGUITTFont.cpp is a wrapper file that includes
 #   additional required headers.
 add_library(cguittfont xCGUITTFont.cpp)
 
+if(FREETYPE_PKGCONFIG_FOUND)
+	set_target_properties(cguittfont
+		PROPERTIES
+		COMPILE_FLAGS "${FREETYPE_CFLAGS}"
+		LINK_FLAGS "${FREETYPE_LDFLAGS}"
+	)
+
+	include_directories(
+	  ${IRRLICHT_INCLUDE_DIR}
+	)
+else(FREETYPE_PKGCONFIG_FOUND)
+	include_directories(
+	  ${IRRLICHT_INCLUDE_DIR}
+	  ${FREETYPE_INCLUDE_DIRS}
+	)
+endif(FREETYPE_PKGCONFIG_FOUND)
+
 target_link_libraries(
-  cguittfont
-  ${IRRLICHT_LIBRARY}
-  ${FREETYPE_LIBRARY}
-  ${ZLIB_LIBRARIES}  # needed by freetype, repeated here for safety
-)
+	cguittfont
+	${IRRLICHT_LIBRARY}
+	${FREETYPE_LIBRARY}
+	${ZLIB_LIBRARIES}  # needed by freetype, repeated here for safety
+	)