Reduce warnings from moc-generated code

- The auto-generated code produces a lot of warnings from
   Clang 8; this obscures the more meaningful warnings from
   actual Calamares code, so tone the warnings down.
 - For Clang, set CALAMARES_MOC_OPTIONS.
 - Add convenience CMake function for automoccing. It applies
   the options as needed to a given target.

CMakeModules/CalamaresAddLibrary.cmake

@@ -44,6 +44,7 @@
 # flag (i.e. `-D`) so only state the name (optionally, also the value)
 # without a `-D` prefixed to it. Pass in a CMake list as needed.
 include( CMakeParseArguments )
+include( CalamaresAutomoc )
 
 function(calamares_add_library)
     # parse arguments (name needs to be saved before passing ARGN into the macro)
@@ -81,10 +82,8 @@ function(calamares_add_library)
         add_library(${target} SHARED ${LIBRARY_SOURCES})
     endif()
 
-    # definitions - can this be moved into set_target_properties below?
-    add_definitions(${QT_DEFINITIONS})
-    set_target_properties(${target} PROPERTIES AUTOMOC TRUE)
-
+    calamares_automoc(${target})
+    
     if(LIBRARY_EXPORT_MACRO)
         set_target_properties(${target} PROPERTIES COMPILE_DEFINITIONS ${LIBRARY_EXPORT_MACRO})
     endif()

CMakeModules/CalamaresAutomoc.cmake

@@ -0,0 +1,36 @@
+# === This file is part of Calamares - <https://github.com/calamares> ===
+#
+#   Calamares is free software: you can redistribute it and/or modify
+#   it under the terms of the GNU General Public License as published by
+#   the Free Software Foundation, either version 3 of the License, or
+#   (at your option) any later version.
+#
+#   Calamares is distributed in the hope that it will be useful,
+#   but WITHOUT ANY WARRANTY; without even the implied warranty of
+#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+#   GNU General Public License for more details.
+#
+#   You should have received a copy of the GNU General Public License
+#   along with Calamares. If not, see <http://www.gnu.org/licenses/>.
+#
+#   SPDX-License-Identifier: GPL-3.0+
+#   License-Filename: LICENSE
+#
+###
+#
+# Helper function for doing automoc on a target.
+#
+# Sets AUTOMOC TRUE for a target.
+#
+# If the global variable CALAMARES_AUTOMOC_OPTIONS is set, uses that
+# as well to set options passed to MOC. This can be used to add
+# libcalamares/utils/moc-warnings.h file to the moc, which in turn
+# reduces compiler warnings in generated MOC code.
+#
+
+function(calamares_automoc TARGET)
+    set_target_properties( ${TARGET} PROPERTIES AUTOMOC TRUE )
+    if ( CALAMARES_AUTOMOC_OPTIONS )
+        set_target_properties( ${TARGET} PROPERTIES AUTOMOC_MOC_OPTIONS "${CALAMARES_AUTOMOC_OPTIONS}" )
+    endif()
+endfunction()