init_priority attribute set by QT_INIT_METAOBJECT gives error on macos gcc 7.3.0

Hello, I encountered some problems when compiling on macos with 5.10.1 version using g++ 7.3.0

error: 'init_priority' attribute is not supported on this platform
{{ QT_INIT_METAOBJECT const QMetaObject nCustomPlotMouseX3Y::staticMetaObject = {}}

it looks like OS X linker ignores the init_priority attribute.

My best guess is that that define should check `SUPPORTS_INIT_PRIORITY` before

https://github.com/gcc-mirror/gcc/blob/master/gcc/config/darwin.h#L957

as stated 

https://gcc.gnu.org/onlinedocs/gccint/Macros-for-Initialization.html

here a link to the build log https://hephaistos.lpp.polytechnique.fr/teamcity/viewLog.html?buildId=12115&buildTypeId=Neutrino_Macos&tab=buildLog&guest=1&_focus=2099