(Bug 555) "Xcode 4.6, ML 10.8.3, Blocks.h fails with errors"

I saw this on bugzilla issue repo.

At eigen/bench/btl/generic_bench/timers/portable_timer.hh:91 there is an include to <CoreServices/CoreServices.h> It is within this (via line 19 -> CoreFoundation.h:43 -> CFBase.h:72) we see #include <Block.h>

This leads to "error: 'XprType' does not refer to a value" when attempting to compile eigen on Mac OS X.