[RFC] libstdc++ atomic_flag changes

[Benjamin Kosnik]

> The issue that I'm trying to solve is that we will have at least two
> targets whose test-and-set insn does not define "set" as 1, as a
> variable of type "bool" would expect.  In the case of Sparc we
> *could* make the test-and-set implementation test for any non-zero
> value, but in the case of m68k the hw will only test-and-set the msb
> of the byte.
> 
> This compiles on x86_64, and is still undergoing testing, but I
> wanted to get this out before Ben quits for the day.  ;-)

Looks fine to me.

-benjamin