Does not compile on my athlon x86 :

make[3]: Entering directory `/var/tmp/portage/gngeo-0.6.7/work/gngeo-0.6.7/src/effect'
i686-pc-linux-gnu-gcc -DHAVE_CONFIG_H -I. -I. -I../.. -I/usr/include/SDL -D_REENTRANT -DI386_ASM -DUSE_STARSCREAM -DUSE_RAZE -O3 -fstrength-reduce -frerun-loop-opt -Wall -Wno-unused -funroll-loops -ffast-math -falign-functions=2 -falign-jumps=2 -fexpensive-optimizations -falign-loops=2 -fschedule-insns2 -malign-double -fomit-frame-pointer -g -fno-strict-aliasing -pipe -mtune=i686 -DCPU=i686 -c sai.c
cc1: error: invalid option `tune=i686'

(I have no "tune" option in my make.conf )