Set QT_NO_EXCEPTIONS when building *.mm files
Review Request #130138 - Created May 25, 2017 and discarded
Apparently, exceptions are disabled when building *.mm files. The alternative would be to set target_compile_options(sonnet_nsspellchecker PRIVATE "-fexceptions") in order to force exception to be on for *.mm files. However, since exceptions aren't used in the code, let's just build without.