gnu: kpackage: Fix build errors in dependent packages.

Fix build errors in dependent packages if PREFIX is different from ECM's
PREFIX - which is the case in Guix.  See <https://bugs.kde.org/424483> for
details.

* gnu/packages/patches/plasma-framework-fix-KF5PackageMacros.cmake.patch: New
  file.
* gnu/local.mk (dist_patch_DATA) Add it.
* packages/kde-frameworks.scm (package)[source]: Use this patch.

gnu/local.mk

@@ -1197,6 +1197,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/kmod-module-directory.patch		\
   %D%/packages/patches/kmscon-runtime-keymap-switch.patch	\
   %D%/packages/patches/kpackage-allow-external-paths.patch	\
+  %D%/packages/patches/kpackage-fix-KF5PackageMacros.cmake.patch \
   %D%/packages/patches/kmplayer-aarch64.patch			\
   %D%/packages/patches/kmplayer-upstream_Fix-build-with-Qt-5.9.patch	\
   %D%/packages/patches/kobodeluxe-paths.patch			\

gnu/packages/kde-frameworks.scm

@@ -1963,7 +1963,8 @@ covers feedback and persistent events.")
                 "03rp7p7i8ihz5wg58gjs638jk7xbszknfiy2j3r979snc57g95mv"))
               ;; Default to: external paths/symlinks can be followed by a
               ;; package
-              (patches (search-patches "kpackage-allow-external-paths.patch"))))
+              (patches (search-patches "kpackage-allow-external-paths.patch"
+                                       "kpackage-fix-KF5PackageMacros.cmake.patch"))))
     (build-system cmake-build-system)
     (native-inputs
      `(("extra-cmake-modules" ,extra-cmake-modules)))

gnu/packages/patches/kpackage-fix-KF5PackageMacros.cmake.patch

@@ -0,0 +1,25 @@
+From 668010ebc9fd84d9dc60f90b9a4ebf3c7054977f Mon Sep 17 00:00:00 2001
+From: Hartmut Goebel <h.goebel@crazy-compilers.com>
+Date: Sun, 25 Oct 2020 20:11:13 +0000
+Subject: [PATCH] Fix build errors if PREFIX is different from ECM's PREFIX.
+
+See <https://bugs.kde.org/424483> for details.
+---
+ KF5PackageMacros.cmake | 3 +--
+ 1 file changed, 1 insertion(+), 2 deletions(-)
+
+diff --git a/KF5PackageMacros.cmake b/KF5PackageMacros.cmake
+index f4c1d1d..acd3798 100644
+--- a/KF5PackageMacros.cmake
++++ b/KF5PackageMacros.cmake
+@@ -1,6 +1,5 @@
+ 
+-find_package(ECM 1.6.0 CONFIG REQUIRED)
+-include(${ECM_KDE_MODULE_DIR}/KDEInstallDirs.cmake)
++include(KDEInstallDirs)
+ 
+ set(KPACKAGE_RELATIVE_DATA_INSTALL_DIR "kpackage")
+ 
+-- 
+GitLab
+