Plural versions of *_INCLUDE_DIR and *_LIBRARY FindMagnum variables.

It took me years to fully accept this CMake policy. Now it's enough to
specify ${MAGNUM_LIBRARIES} instead of all those Corrade, OpenGL /
OpenGL ES, GLEW etc. dependencies (heh).

modules/FindMagnum.cmake

@@ -10,8 +10,9 @@
 #  MAGNUM_TARGET_GLES           - Defined if Magnum was built for OpenGL ES,
 #   slightly reducing feature count. The same variable is also #defined in
 #   Magnum headers.
-#  MAGNUM_LIBRARY               - Magnum library
-#  MAGNUM_INCLUDE_DIR           - Root include dir
+#  MAGNUM_LIBRARIES             - Magnum library and dependent libraries
+#  MAGNUM_INCLUDE_DIRS          - Root include dir and include dirs of
+#   dependencies
 #  MAGNUM_PLUGINS_IMPORTER_DIR  - Directory with importer plugins
 #
 # This command will try to find only the base library, not the optional
@@ -35,10 +36,14 @@
 # For each component is then defined:
 #
 #  MAGNUM_*_FOUND   - Whether the component was found
-#  MAGNUM_*_LIBRARY - Component library
+#  MAGNUM_*_LIBRARIES - Component library and dependent libraries
 #
 # Additionally these variables are defined for internal usage:
 #
+#  MAGNUM_INCLUDE_DIR                   - Root include dir (w/o dependencies)
+#  MAGNUM_LIBRARY                       - Magnum library (w/o dependencies)
+#  MAGNUM_*_LIBRARY                     - Component libraries (w/o dependencies)
+#
 #  MAGNUM_LIBRARY_INSTALL_DIR           - Library installation directory
 #  MAGNUM_PLUGINS_INSTALL_DIR           - Plugin installation directory
 #  MAGNUM_PLUGINS_IMPORTER_INSTALL_DIR  - Importer plugin installation directory
@@ -91,7 +96,9 @@ foreach(component ${Magnum_FIND_COMPONENTS})
         # GLUT context dependencies
         if(${component} STREQUAL GlutContext)
             find_package(GLUT)
-            if(NOT GLUT_FOUND)
+            if(GLUT_FOUND)
+                set(_MAGNUM_${_COMPONENT}_LIBRARIES ${GLUT_LIBRARIES})
+            else()
                 unset(MAGNUM_${_COMPONENT}_LIBRARY)
             endif()
         endif()
@@ -99,7 +106,9 @@ foreach(component ${Magnum_FIND_COMPONENTS})
         # SDL2 context dependencies
         if(${component} STREQUAL Sdl2Context)
             find_package(SDL2)
-            if(NOT SDL2_FOUND)
+            if(SDL2_FOUND)
+                set(_MAGNUM_${_COMPONENT}_LIBRARIES ${SDL2_LIBRARY})
+            else()
                 unset(MAGNUM_${_COMPONENT}_LIBRARY)
             endif()
         endif()
@@ -108,7 +117,9 @@ foreach(component ${Magnum_FIND_COMPONENTS})
         if(${component} STREQUAL EglContext)
             find_package(EGL)
             find_package(X11)
-            if(NOT EGL_FOUND OR NOT X11_FOUND)
+            if(EGL_FOUND AND X11_FOUND)
+                set(_MAGNUM_${_COMPONENT}_LIBRARIES ${EGL_LIBRARY} ${X11_LIBRARIES})
+            else()
                 unset(MAGNUM_${_COMPONENT}_LIBRARY)
             endif()
         endif()
@@ -143,6 +154,7 @@ foreach(component ${Magnum_FIND_COMPONENTS})
 
     # Decide if the library was found
     if(MAGNUM_${_COMPONENT}_LIBRARY AND _MAGNUM_${_COMPONENT}_INCLUDE_DIR)
+        set(MAGNUM_${_COMPONENT}_LIBRARIES ${MAGNUM_${_COMPONENT}_LIBRARY} ${_MAGNUM_${_COMPONENT}_LIBRARIES})
         set(Magnum_${component}_FOUND TRUE)
     else()
         set(Magnum_${component}_FOUND FALSE)
@@ -154,6 +166,21 @@ find_package_handle_standard_args(Magnum
     REQUIRED_VARS MAGNUM_INCLUDE_DIR MAGNUM_LIBRARY
     HANDLE_COMPONENTS)
 
+# Dependent libraries and includes
+set(MAGNUM_INCLUDE_DIRS ${MAGNUM_INCLUDE_DIR}
+    ${CORRADE_INCLUDE_DIR})
+set(MAGNUM_LIBRARIES ${MAGNUM_LIBRARY}
+    ${CORRADE_UTILITY_LIBRARY}
+    ${CORRADE_PLUGINMANAGER_LIBRARY})
+if(NOT MAGNUM_TARGET_GLES)
+    set(MAGNUM_LIBRARIES ${MAGNUM_LIBRARIES}
+        ${OPENGL_gl_LIBRARY}
+        ${GLEW_LIBRARY})
+else()
+    set(MAGNUM_LIBRARIES ${MAGNUM_LIBRARIES}
+        ${OPENGLES2_LIBRARY})
+endif()
+
 # Installation dirs
 set(MAGNUM_LIBRARY_INSTALL_DIR ${CMAKE_INSTALL_PREFIX}/lib${LIB_SUFFIX})
 set(MAGNUM_PLUGINS_INSTALL_DIR ${MAGNUM_LIBRARY_INSTALL_DIR}/magnum)
@@ -162,6 +189,8 @@ set(MAGNUM_CMAKE_MODULE_INSTALL_DIR ${CMAKE_ROOT}/Modules)
 set(MAGNUM_INCLUDE_INSTALL_DIR ${CMAKE_INSTALL_PREFIX}/include/Magnum)
 set(MAGNUM_PLUGINS_INCLUDE_INSTALL_DIR ${CMAKE_INSTALL_PREFIX}/include/Magnum/Plugins)
 mark_as_advanced(FORCE
+    MAGNUM_LIBRARY
+    MAGNUM_INCLUDE_DIR
     MAGNUM_LIBRARY_INSTALL_DIR
     MAGNUM_PLUGINS_INSTALL_DIR
     MAGNUM_PLUGINS_IMPORTER_INSTALL_DIR