Set includes and libs on object targets

Instead of using the global `include_directories()` and
`link_libraries()` calls use the target versions
`target_include_directories()` and `target_include_libraries()` with
`PRIVATE` keyword instead.

The dependencies are libraries only, the headers are added to the build
instructions in a separate call. So the `target_link_libraries()` calls
are not needed for the object-libraries to be built.

source/Irrlicht/CMakeLists.txt

@@ -64,8 +64,7 @@ else()
 	find_package(X11 REQUIRED)
 endif()
 
-# Includes for object libraries.
-include_directories(
+set(link_includes
 	"${PROJECT_SOURCE_DIR}/include"
 	"${CMAKE_CURRENT_SOURCE_DIR}"
 
@@ -81,7 +80,6 @@ include_directories(
 	${X11_INCLUDE_DIR}
 )
 
-# Libraries for object libraries.
 set(link_libs
 	"${ZLIB_LIBRARY}"
 	"${JPEG_LIBRARY}"
@@ -100,7 +98,6 @@ set(link_libs
 	${X11_X11_LIB}
 	${X11_Xxf86vm_LIB}
 )
-link_libraries(${link_libs})
 
 # Source files
 
@@ -401,18 +398,15 @@ add_library(IRRGUIOBJ OBJECT
 
 option(BUILD_SHARED_LIBS "Build shared library" TRUE)
 
-# IrrlichtMt target
-add_library(IrrlichtMt
-	$<TARGET_OBJECTS:IRRMESHOBJ>
-	$<TARGET_OBJECTS:IRROBJ>
-	$<TARGET_OBJECTS:IRRPARTICLEOBJ>
-	$<TARGET_OBJECTS:IRRANIMOBJ>
-	$<TARGET_OBJECTS:IRRVIDEOOBJ>
-	$<TARGET_OBJECTS:IRRSWRENDEROBJ>
-	$<TARGET_OBJECTS:IRRIOOBJ>
-	$<TARGET_OBJECTS:IRROTHEROBJ>
-	$<TARGET_OBJECTS:IRRGUIOBJ>
-)
+add_library(IrrlichtMt)
+foreach(object_lib
+	IRRMESHOBJ IRROBJ IRRPARTICLEOBJ IRRANIMOBJ IRRVIDEOOBJ IRRSWRENDEROBJ
+	IRRIOOBJ IRROTHEROBJ IRRGUIOBJ)
+	# Set include directories for object library compilation
+	target_include_directories(${object_lib} PRIVATE ${link_includes})
+	# Add objects from object library to main library
+	target_sources(IrrlichtMt PRIVATE $<TARGET_OBJECTS:${object_lib}>)
+endforeach()
 
 # Alias target provides add_submodule compatibility
 add_library(IrrlichtMt::IrrlichtMt ALIAS IrrlichtMt)
@@ -423,16 +417,7 @@ target_include_directories(IrrlichtMt
 		"$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>"
 		"$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}/irrlichtmt>"
 	PRIVATE
-		"${ZLIB_INCLUDE_DIR}"
-		"${JPEG_INCLUDE_DIR}"
-		"${PNG_INCLUDE_DIR}"
-
-		${OPENGL_INCLUDE_DIR}
-		${OPENGLES2_INCLUDE_DIR}
-		${EGL_INCLUDE_DIR}
-
-		"$<$<PLATFORM_ID:Android>:${ANDROID_NDK}/sources/android/native_app_glue>"
-		${X11_INCLUDE_DIR}
+		${link_includes}
 )
 
 target_link_libraries(IrrlichtMt PRIVATE ${link_libs})