Fix mcontext_t sigcontext namespace (bug 21457).

Fix mcontext_t sigcontext namespace (bug 21457).

This patch completes the ucontext.h namespace fixes by fixing issues
related to the use of struct sigcontext as mcontext_t, and inclusion
of <bits/sigcontext.h> even when struct sigcontext is not so used.

Inclusion of <bits/sigcontext.h> by <sys/ucontext.h> is removed; the
way to get the sigcontext structure is by including <signal.h> (in a
context where __USE_MISC is defined); the sysdeps/generic version of
sys/ucontext.h keeps the inclusion by necessity, with a comment about
how this is not namespace-clean, but the only configuration that used
it, MicroBlaze, gets its own version of the header in this patch.
Where mcontext_t was typedefed to struct sigcontext, the contents of
struct sigcontext are inserted (with appropriate namespace handling to
prefix fields with __ when __USE_MISC is not defined); review should
check that this has been done correctly in each case, whether the
definition of struct sigcontext comes from glibc headers or from the
Linux kernel.  This changes C++ name mangling on affected
architectures (which do not include x86_64/x86).

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

2017-08-14  Joseph Myers  <joseph@codesourcery.com>

	[BZ #21457]
	* sysdeps/arm/sys/ucontext.h: Do not include <bits/sigcontext.h>.
	* sysdeps/generic/sys/ucontext.h: Add comment about use of struct
	sigcontext and namespace requirements.
	* sysdeps/i386/sys/ucontext.h: Do not include <bits/sigcontext.h>.
	* sysdeps/m68k/sys/ucontext.h: Likewise.
	* sysdeps/mips/sys/ucontext.h: Likewise.  Include <bits/types.h>.
	* sysdeps/unix/sysv/linux/aarch64/sys/ucontext.h: Do not include
	<bits/sigcontext.h>.
	(__ctx): Define earlier.
	(mcontext_t): Define structure contents rather than using struct
	sigcontext.
	* sysdeps/unix/sysv/linux/aarch64/ucontext_i.sym (oEXTENSION): Use
	__glibc_reserved1 instead of __reserved.
	* sysdeps/unix/sysv/linux/alpha/sys/ucontext.h: Do not include
	<bits/sigcontext.h>.
	(__ctx): Define earlier.
	(mcontext_t): Define structure contents rather than using struct
	sigcontext.
	* sysdeps/unix/sysv/linux/alpha/ucontext-offsets.sym: Use
	mcontext_t instead of struct sigcontext.
	* sysdeps/unix/sysv/linux/arm/sys/ucontext.h: Do not include
	<bits/sigcontext.h>.
	(__ctx): Define earlier.
	(mcontext_t): Define structure contents rather than using struct
	sigcontext.
	* sysdeps/unix/sysv/linux/hppa/sys/ucontext.h: Do not include
	<bits/sigcontext.h>.
	(__ctx): Define earlier.
	(mcontext_t): Define structure contents rather than using struct
	sigcontext.
	* sysdeps/unix/sysv/linux/ia64/makecontext.c (__makecontext): Use
	mcontext_t instead of struct sigcontext.
	* sysdeps/unix/sysv/linux/ia64/sigcontext-offsets.sym: Use
	mcontext_t instead of struct sigcontext.
	* sysdeps/unix/sysv/linux/ia64/sys/ucontext.h: Do not include
	<bits/sigcontext.h>.
	(__ctx): New macro.
	(struct __ia64_fpreg_mcontext): New type.
	(mcontext_t): Define structure contents rather than using struct
	sigcontext.
	(_SC_GR0_OFFSET): Use mcontext_t instead of struct sigcontext.
	(uc_sigmask): Define using __ctx.
	(uc_stack): Likewise.
	* sysdeps/unix/sysv/linux/ia64/sys/procfs.h: Include
	<bits/sigcontext.h>.
	* sysdeps/unix/sysv/linux/ia64/sys/ptrace.h: Likewise.
	* sysdeps/unix/sysv/linux/m68k/sys/ucontext.h: Do not include
	<bits/sigcontext.h>.
	* sysdeps/unix/sysv/linux/microblaze/sys/ucontext.h: New file.
	* sysdeps/unix/sysv/linux/mips/sys/ucontext.h: Do not include
	<bits/sigcontext.h>.
	* sysdeps/unix/sysv/linux/nios2/sys/ucontext.h: Do not include
	<bits/sigcontext.h>.
	* sysdeps/unix/sysv/linux/powerpc/sys/ucontext.h: Do not include
	<bits/sigcontext.h>.
	* sysdeps/unix/sysv/linux/s390/sys/ucontext.h: Do not include
	<bits/sigcontext.h>.
	* sysdeps/unix/sysv/linux/sh/sys/ucontext.h: Do not include
	<bits/sigcontext.h>.
	* sysdeps/unix/sysv/linux/sparc/sys/ucontext.h: Do not include
	<bits/sigcontext.h>.
	* sysdeps/unix/sysv/linux/tile/sys/ucontext.h: Do not include
	<bits/sigcontext.h>.
	(__ctx): Define earlier.
	(mcontext_t): Define structure contents rather than using struct
	sigcontext.
	* sysdeps/unix/sysv/linux/x86/sys/ucontext.h: Do not include
	<bits/sigcontext.h>.  Include <bits/types.h>.
	* conform/Makefile (test-xfail-XPG42/signal.h/conform): Remove.
	(test-xfail-XPG42/sys/wait.h/conform): Likewise.
	(test-xfail-XPG42/ucontext.h/conform): Likewise.
	(test-xfail-UNIX98/signal.h/conform): Likewise.
	(test-xfail-UNIX98/sys/wait.h/conform): Likewise.
	(test-xfail-UNIX98/ucontext.h/conform): Likewise.
	(test-xfail-XOPEN2K/signal.h/conform): Likewise.
	(test-xfail-XOPEN2K/sys/wait.h/conform): Likewise.
	(test-xfail-XOPEN2K/ucontext.h/conform): Likewise.
	(test-xfail-POSIX2008/signal.h/conform): Likewise.
	(test-xfail-POSIX2008/sys/wait.h/conform): Likewise.
	(test-xfail-XOPEN2K8/signal.h/conform): Likewise.
	(test-xfail-XOPEN2K8/sys/wait.h/conform): Likewise.