defconfigs: disable CONFIG_CC_OPTIMIZE_FOR_SIZE

With GCC releases before 4.8, using -Os causes the compiler to ignore
Linux's likely()/unlikely() branch profiling hints, which more than
wipes out any gains we get from reduced icache footprint.  See
http://lwn.net/Articles/534735/ and
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54364 .