If you try to build stage2 of V1.2 on a K6 or i586 the build at some point transistions to building a i686 machine as evedent in seeing the -m=i686 lines going by on the screen. The build fails the first time a i686 instruction is tired. V1.1A is building just fine on the same hardware.
The default flags in make.conf have changed to i686 flags, so read the manual and actually change the flags in make.conf to the k5/pentium flags. Of course it is debateable what the default should be.
Like Paul said, read the installation docs :P
Seems like instead of using a default build target that breaks on lots of hardware and then chiding people who (like most bleeding-edge enthusiasts) build first and read later, someone should add some code to emerge to determine the cpu class and then issue a warning and automatically change the build target when there is a mismatch. My /proc/cpuinfo shows: processor : 0 vendor_id : AuthenticAMD cpu family : 5 model : 8 model name : AMD-K6(tm) 3D processor stepping : 12 cpu MHz : 551.065 cache size : 64 KB fdiv_bug : no hlt_bug : no f00f_bug : no coma_bug : no fpu : yes fpu_exception : yes cpuid level : 1 wp : yes flags : fpu vme de pse tsc msr mce cx8 pge mmx syscall 3dnow k6_mtrr bogomips : 1089.53 so there's all sorts of information available there.
why ? a warning we create today may be invalid tomorrow ... its just another place to maintain documentation ...