QML modules: Add a way to suppress ranlib's "file ... has no symbols" warnings

Using qt_add_qml_module() to generate a static library can generate warnings about something that's a non-issue:

.../usr/bin/ranlib: file: qml/libmyqmlmoduleplugin.a(mocs_compilation.cpp.o) has no symbols

Suggestion

Let the CMake QML API automatically add the "-no_warning_for_no_symbols" flag

See also (other places which use this flag)

• https://code.qt.io/cgit/qt/qtbase.git/tree/mkspecs/features/mac/no_warn_empty_obj_files.prf
• https://code.qt.io/cgit/qt/qtbase.git/tree/cmake/QtBuild.cmake?h=wip/cmake#n319