When building Qt, LLVM linker issues warnings like this for some of the tools:

ld: warning: direct access in function 'QHash<QString, int>::insert(QString const&, int const&)' from file '/Users/macos/QtBuild/qtbase/lib/libQt5Bootstrap.a(qcommandlineparser.o)' to global weak symbol 'QHash<QString, int>::deleteNode2(QHashData::Node*)' from file '.obj/rcc.o' means the weak symbol cannot be overridden at runtime. This was likely caused by different translation units being compiled with different visibility settings.

Warnings are available in the logs in the attachement. Reproduces on 5.12.4 and 5.12.6.

Build commands:

git clone git://code.qt.io/qt/qt5.git

cd qt5/

git checkout 5.12.4

perl init-repository --module-subset=qtbase,qtmacextras,qttools,qttranslations,qtdeclarative

cd ../QtBuild/

../qt5/configure -opensource -confirm-license -shared -nomake tests -nomake examples -silent -debug -platform macx-clang -opengl desktop -no-dbus -no-framework

make