CMake: Don't use exported SDK libs if present in current build

Once installed, CMake will find the SDK libs in the installation
location (at least on Windows). This should ensure that the libs
from the current build are used, if they are present.

doomsday/sdk/libappfw/DengAppfwConfig.cmake

@@ -1,6 +1,10 @@
+find_package (Qt5Widgets REQUIRED)
 find_package (DengCore REQUIRED)
 find_package (DengGui REQUIRED)
 find_package (DengShell REQUIRED)
-find_package (Qt5Widgets REQUIRED)
 
-include ("${CMAKE_CURRENT_LIST_DIR}/DengAppfw.cmake")
+# Deng::libappfw may exist in the current build, in which case using 
+# a previously installed version is inappropriate.
+if (NOT TARGET Deng::libappfw)
+    include ("${CMAKE_CURRENT_LIST_DIR}/DengAppfw.cmake")
+endif ()

doomsday/sdk/libcore/DengCoreConfig.cmake

@@ -1,6 +1,9 @@
-find_package (Qt5Core)
-find_package (Qt5Network)
+find_package (Qt5 COMPONENTS Core Network REQUIRED)
 
-include ("${CMAKE_CURRENT_LIST_DIR}/DengCore.cmake")
+# Deng::libcore may exist in the current build, in which case using 
+# a previously installed version is inappropriate.
+if (NOT TARGET Deng::libcore)
+    include ("${CMAKE_CURRENT_LIST_DIR}/DengCore.cmake")
+endif ()
 
 list (APPEND DENG_REQUIRED_PACKAGES net.dengine.stdlib)

doomsday/sdk/libgui/DengGuiConfig.cmake

@@ -1,7 +1,10 @@
+find_package (Qt5 COMPONENTS Gui OpenGL REQUIRED)
 find_package (DengCore REQUIRED)
-find_package (Qt5Gui REQUIRED)
-find_package (Qt5OpenGL REQUIRED)
 
-include ("${CMAKE_CURRENT_LIST_DIR}/DengGui.cmake")
+# Deng::libgui may exist in the current build, in which case using 
+# a previously installed version is inappropriate.
+if (NOT TARGET Deng::libgui)
+    include ("${CMAKE_CURRENT_LIST_DIR}/DengGui.cmake")
+endif ()
 
 list (APPEND DENG_REQUIRED_PACKAGES net.dengine.stdlib.gui)

doomsday/sdk/liblegacy/DengLegacyConfig.cmake

@@ -1,3 +1,7 @@
-find_package (DengCore REQUIRED)
+find_package (DengCore REQUIRED)    
 
-include ("${CMAKE_CURRENT_LIST_DIR}/DengLegacy.cmake")
+# Deng::liblegacy may exist in the current build, in which case using 
+# a previously installed version is inappropriate.
+if (NOT TARGET Deng::liblegacy)
+    include ("${CMAKE_CURRENT_LIST_DIR}/DengLegacy.cmake")
+endif ()

doomsday/sdk/libshell/DengShellConfig.cmake

@@ -1,3 +1,7 @@
 find_package (DengCore REQUIRED)
 
-include ("${CMAKE_CURRENT_LIST_DIR}/DengShell.cmake")
+# Deng::libshell may exist in the current build, in which case using 
+# a previously installed version is inappropriate.
+if (NOT TARGET Deng::libshell)
+    include ("${CMAKE_CURRENT_LIST_DIR}/DengShell.cmake")
+endif ()