CMake: Fix usage of qt_process_qlalr when cross compiling

qtremoteobjects has a tool that uses qt_process_qlalr. The function
doesn't have a check to see if the consuming target is an imported
target, to skip doing any work when corss compiling.

Fix it, like we do in qt_extend_target.

Change-Id: Ide389a371aa07225f08689d15125c04d8b0e3916
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>

cmake/QtBuild.cmake

@@ -5090,6 +5090,12 @@ endfunction()
 # 'input_file_list' is a list of 'foo.g' file paths.
 # 'flags' are extra flags to be passed to qlalr.
 function(qt_process_qlalr consuming_target input_file_list flags)
+    # Don't try to extend_target when cross compiling an imported host target (like a tool).
+    qt_is_imported_target("${consuming_target}" is_imported)
+    if(is_imported)
+        return()
+    endif()
+
     foreach(input_file ${input_file_list})
         file(STRINGS ${input_file} input_file_lines)
         qt_qlalr_find_option_in_list("${input_file_lines}" "^%parser(.+)" "parser")