Fix the generated qxmpp pkgconfig files

The include directory and link targets changed.
Also add a backward compatible pkgconfig file for Qt5 builds.

CMakeLists.txt

@@ -126,16 +126,16 @@ install(
 )
 
 # Generate QXmppQt5/6.pc
-configure_file(${CMAKE_CURRENT_SOURCE_DIR}/qxmpp.pc.in ${CMAKE_CURRENT_BINARY_DIR}/qxmpp.pc @ONLY)
+configure_file(${CMAKE_CURRENT_SOURCE_DIR}/qxmpp.pc.in ${CMAKE_CURRENT_BINARY_DIR}/${QXMPP_TARGET}.pc @ONLY)
 install(
-    FILES ${CMAKE_CURRENT_BINARY_DIR}/qxmpp.pc
-    RENAME QXmppQt${QT_VERSION_MAJOR}.pc
+    FILES ${CMAKE_CURRENT_BINARY_DIR}/${QXMPP_TARGET}.pc
     DESTINATION "${CMAKE_INSTALL_LIBDIR}/pkgconfig"
     COMPONENT Devel
 )
 
 # "qxmpp.pc" for backwards-compatibility
 if(QT_VERSION_MAJOR EQUAL 5)
+    configure_file(${CMAKE_CURRENT_SOURCE_DIR}/qxmpp_legacy.pc.in ${CMAKE_CURRENT_BINARY_DIR}/qxmpp.pc @ONLY)
     install(
         FILES ${CMAKE_CURRENT_BINARY_DIR}/qxmpp.pc
         DESTINATION "${CMAKE_INSTALL_LIBDIR}/pkgconfig"

qxmpp.pc.in

@@ -5,13 +5,13 @@
 prefix=@CMAKE_INSTALL_PREFIX@
 exec_prefix=${prefix}
 libdir=@CMAKE_INSTALL_FULL_LIBDIR@
-includedir=@CMAKE_INSTALL_FULL_INCLUDEDIR@/qxmpp
+includedir=@CMAKE_INSTALL_FULL_INCLUDEDIR@/@QXMPP_TARGET@
 
 
-Name: Qxmpp
+Name: @QXMPP_TARGET@
 Description: QXmpp Library
 Version: @PROJECT_VERSION@
-Libs: -lqxmpp
-Libs.private: -lQt5Network -lQt5Xml -lQt5Core
+Libs: -l@QXMPP_TARGET@
+Libs.private: -lQt@QT_VERSION_MAJOR@Network -lQt@QT_VERSION_MAJOR@Xml -lQt@QT_VERSION_MAJOR@Core
 Cflags: -I${includedir}
 

qxmpp_legacy.pc.in

@@ -0,0 +1,17 @@
+# SPDX-FileCopyrightText: 2017 Niels Ole Salscheider <[email protected]>
+#
+# SPDX-License-Identifier: CC0-1.0
+
+prefix=@CMAKE_INSTALL_PREFIX@
+exec_prefix=${prefix}
+libdir=@CMAKE_INSTALL_FULL_LIBDIR@
+includedir=@CMAKE_INSTALL_FULL_INCLUDEDIR@/QXmppQt5
+
+
+Name: Qxmpp
+Description: QXmpp Library
+Version: @PROJECT_VERSION@
+Requires: QXmppQt5
+Libs: -lQXmppQt5
+Cflags: -I${includedir}
+