pthread_md.h. This commit only moves the definition; it does not
change it for any of the platforms. This more easily allows 64-bit
architectures (in particular) to pick a slightly larger stack size.
instead of long types for low-level locks.
Add prototypes for some internal libc functions that are
wrapped by the library as cancellation points.
Add memory barriers to alpha atomic swap functions (submitted
by davidxu).
Requested by: bde
