Compiling with CHOST="x86_64-apple-darwin12" aborts. Compiling with CHOST="x86_64-apple-darwin11" works fine. Reproducible: Always
Happens on Mountain Lion 10.8: Darwin 12.0.0 Darwin Kernel Version 12.0.0: Mon Aug 6 18:24:39 PDT 2012; root:xnu-2050.9.1~1/RELEASE_X86_64 x86_64 i386 MacBookAir3,2 Darwin
Created attachment 320956 [details] emerge --info
Created attachment 320958 [details] build.log
The fix was already in the ebuild for Lion, so now it's extended to Mountain Lion.