kde: ECMPoQmTools — make LinguistTools optional (cross-build without qttools)

ecm_process_po_files_as_qm() did find_package(Qt6 COMPONENTS LinguistTools
REQUIRED) for lrelease/lconvert. Those live in qttools, which is not in the
Redox cross toolchain, so every KDE package that installs translations failed to
configure (Qt6_FOUND=FALSE). Use OPTIONAL_COMPONENTS (so a missing LinguistTools
neither aborts nor registers as a required package the final feature_summary
fails on) and return early when the tools are absent — .po -> .qm compilation is
skipped and the app builds untranslated. Systemic: unblocks all KF6 packages.

local/recipes/kde/kf6-extra-cmake-modules/source/modules/ECMPoQmTools.cmake

@@ -148,11 +148,21 @@ function(ecm_process_po_files_as_qm lang)
         message(FATAL_ERROR "ecm_process_po_files_as_qm() must be called with PO_FILES argument")
     endif()
 
-    # Find lrelease and lconvert
+    # Find lrelease and lconvert. LinguistTools (lrelease/lconvert) live in
+    # qttools, which is not part of the cross toolchain when building for Redox.
+    # Use OPTIONAL_COMPONENTS so a missing LinguistTools neither aborts here nor
+    # registers as a required package that the final feature_summary would fail
+    # on. Without the tools, .po -> .qm translation compilation cannot run, so
+    # skip it gracefully (the app is built untranslated).
     if (QT_MAJOR_VERSION EQUAL "5")
-        find_package(Qt5LinguistTools CONFIG REQUIRED)
+        find_package(Qt5LinguistTools CONFIG)
     else()
-        find_package(Qt6 COMPONENTS LinguistTools CONFIG REQUIRED)
+        find_package(Qt6 OPTIONAL_COMPONENTS LinguistTools CONFIG)
+    endif()
+
+    if (NOT TARGET Qt${QT_MAJOR_VERSION}::lconvert AND NOT TARGET Qt${QT_MAJOR_VERSION}::lrelease)
+        message(STATUS "ECMPoQmTools: LinguistTools unavailable; skipping .po -> .qm processing")
+        return()
     endif()
 
     if(TARGET Qt${QT_MAJOR_VERSION}::lconvert)