Complete sys/procfs.h unification.

Complete sys/procfs.h unification.

This patch completes the process of unifying sys/procfs.h headers for
architectures using the Linux kernel by making alpha use the generic
version.

That was previously deferred because alpha has different definitions
of prgregset_t and prfpregset_t from other architectures, so changing
to the common definitions would change C++ name mangling.  To avoid
such a change, a header bits/procfs-prregset.h is added, and alpha
gets its own version of that header.

Tested for x86_64 and x86, and with build-many-glibcs.py.

	* sysdeps/unix/sysv/linux/sys/procfs.h: Include
	<bits/procfs-prregset.h>.
	(prgregset_t): Define using __prgregset_t.
	(prfpregset_t): Define using __prfpregset_t.
	* sysdeps/unix/sysv/linux/Makefile [$(subdir) = misc]
	(sysdep_headers): Add bits/procfs-prregset.h.
	* sysdeps/unix/sysv/linux/bits/procfs-prregset.h: New file.
	* sysdeps/unix/sysv/linux/alpha/bits/procfs-prregset.h: Likewise.
	* sysdeps/unix/sysv/linux/alpha/bits/procfs.h: Likewise.
	* sysdeps/unix/sysv/linux/alpha/sys/procfs.h: Remove file.