QT_BUILD_KEY in qconfig.h should be architecture dependent on linux

I'm using ArchLinux x86_64 with Qt 4.8.5-1.

My application is x86 and contains plugins. I can compile plugins for my application but QPluginLoader tells me:

The plugin X uses incompatible Qt library. Expected build key "i386 linux g+-4 full-config", got "x86_64 linux g+-4 full-config"

in /usr/include/qt4/QtCore/qconfig.h I found:

#define QT_BUILD_KEY "x86_64 linux g++-4 full-config"
#define QT_BUILD_KEY_COMPAT "x86_64 Linux g++-4 full-config"

but when I change it to:

#ifdef _x86_64_
#define QT_BUILD_KEY "x86_64 linux g++-4 full-config"
#define QT_BUILD_KEY_COMPAT "x86_64 Linux g++-4 full-config"
#elif _i386_
#define QT_BUILD_KEY "i386 linux g++-4 full-config"
#define QT_BUILD_KEY_COMPAT "i386 Linux g++-4 full-config"
#endif

then my application can load plugin properly.