PI mutex support for pthread_cond_* now in nptl

[Roland McGrath]

At least the x86 assembly versions were written because the code produced
by GCC at the time was drastically worse.  But that was long ago.  We now
mandate compiling with GCC 4.3 or newer and recommend 4.6 or newer, so it
merits examining the code produced by those compilers and reconsidering the
judgments of the past.  But we will be conservative and not drop any
hand-written assembly unless recent compilers at -O2 are demonstrated to
produce code at least as good.  (Perhaps the reasonable standard is
something like at least as good from 4.6 -O3 and not a whole lot worse from
4.3 -O2.)  As time goes on, we can of course examine then-common compilers
and reconsider these judgments.  As of now, even 4.7 is not common yet.


Thanks,
Roland