libpcre and libColladaDOM produce faulty "file has no symbols" warnings with XCode

Due to QTBUG-44726 building libpcre and libColladaDOM on macOS produces "file <filename> has no symbols" warnings. At the moment there seems to be no way to suppress these unnecessary warnings, but once the related bug is fixed there should be a way to get rid of those and then at some point enable warnings as errors.

Following statically linked libraries throw these warnings:

• qtbase/lib/libpcre_debug.a (pcre_string_utils.o)
• qtbase/lib/libpcre.a (pcre_string_utils.o)
• qtbase/lib/libColladaDOM_debug.a (daeZAEUncompressHandler.o)
• qtbase/lib/libColladaDOM.a (daeZAEUncompressHandler.o)
• ../../../lib/libCommonLib_debug.a (Mutex.o)
• ../../../lib/libCommonLib.a (Mutex.o)