Created attachment 385134 [details] backtrace with CFLAGS="-march=pentium4 -O1 -fno-omit-frame-pointer -g -ggdb -pipe" All graphical GNUstep applications segfault, with gnustep-base/gnustep-gui-0.24.0, sys-devel/clang-3.4.2-r100 and gnustep-base/libobjc2-1.7, when gnustep-gui is built with -march=pentium4 or -march=native. This bug doesn't occur when -march=i686 or -march=i686 -mtune=pentium4/native is used. Maybe a compiler bug?
Created attachment 385136 [details] emerge --info '=gnustep-base/gnustep-gui-0.24.0'
Created attachment 385138 [details] emerge -pqv '=gnustep-base/gnustep-gui-0.24.0'
Created attachment 385140 [details] Config log of =gnustep-base/gnustep-gui-0.24.0
Created attachment 385142 [details] Build log of =gnustep-base/gnustep-gui-0.24.0
Sorry, small correction. It's not clang-3.4.2-r100, but clang-3.3-r100 was used.
Bug persists with clang-3.5.0-r100.
Cleaning old bugs, with all changes to clang (and also gnustep), this one most likely disappeared some time ago. Don't hesitate to reopen if this is not the case!