XCode builds with -fvisibility=hidden which differs from macx-g++

The XCode make spec file macx-xcode creates projects that by default add -fvisibility=hidden to the make command, while a Makefile created by macx-g++ doesn't mention -fvisibility, so it's treated as -fvisibility=default.

This seems to be a known issue with XCode,

http://osdir.com/ml/finance.quantlib.user/2007-11/msg00054.html

but it would be nice if the XCode project created by Qt was able to build in the same way
as the macx-g++