Fix GCC 11 -Warray-parameter warning for __sigsetjmp (bug 26647)

This patch fixes part of bug 26647 (-Werror=array-parameter error
building with GCC 11 because of __sigsetjmp being declared using an
array parameter in one header and a pointer parameter in another).

The fix is to split the struct __jmp_buf_tag definition out to a
separate bits/types/ header so it can be included in pthread.h, so
that pthread.h can declare __sigsetjmp with the type contents visible,
so can use an array (as in setjmp.h) rather than a pointer in the
declaration.

Note that several other build failures with GCC 11 remain.  This does
not fix the jmp_buf-related -Wstringop-overflow errors (also discussed
in bug 26647), or -Warray-parameter errors for other functions (bug
26686), or -Warray-bounds errors (bug 26687).

Tested, with older compilers, natively for x86_64 and with
build-many-glibc.py for aarch64-linux-gnu.  Tested with
build-many-glibcs.py with GCC mainline for aarch64-linux-gnu that this
gets past the -Warray-parameter issue for __sigsetjmp (with the next
build failure being the other one discussed in bug 26647).

include/bits/types/struct___jmp_buf_tag.h

@@ -0,0 +1 @@
+#include <setjmp/bits/types/struct___jmp_buf_tag.h>

setjmp/Makefile

@@ -22,7 +22,8 @@ subdir	:= setjmp
 
 include ../Makeconfig
 
-headers	:= setjmp.h bits/setjmp.h bits/setjmp2.h
+headers	:= setjmp.h bits/setjmp.h bits/setjmp2.h \
+	   bits/types/struct___jmp_buf_tag.h
 
 routines	:= setjmp sigjmp bsd-setjmp bsd-_setjmp \
 		   longjmp __longjmp jmp-unwind

setjmp/bits/types/struct___jmp_buf_tag.h

@@ -0,0 +1,37 @@
+/* Define struct __jmp_buf_tag.
+   Copyright (C) 1991-2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#ifndef	__jmp_buf_tag_defined
+#define	__jmp_buf_tag_defined 1
+
+#include <bits/setjmp.h>		/* Get `__jmp_buf'.  */
+#include <bits/types/__sigset_t.h>
+
+/* Calling environment, plus possibly a saved signal mask.  */
+struct __jmp_buf_tag
+  {
+    /* NOTE: The machine-dependent definitions of `__sigsetjmp'
+       assume that a `jmp_buf' begins with a `__jmp_buf' and that
+       `__mask_was_saved' follows it.  Do not move these members
+       or add others before it.  */
+    __jmp_buf __jmpbuf;		/* Calling environment.  */
+    int __mask_was_saved;	/* Saved the signal mask?  */
+    __sigset_t __saved_mask;	/* Saved signal mask.  */
+  };
+
+#endif

setjmp/setjmp.h

@@ -27,20 +27,7 @@
 __BEGIN_DECLS
 
 #include <bits/setjmp.h>		/* Get `__jmp_buf'.  */
-#include <bits/types/__sigset_t.h>
-
-/* Calling environment, plus possibly a saved signal mask.  */
-struct __jmp_buf_tag
-  {
-    /* NOTE: The machine-dependent definitions of `__sigsetjmp'
-       assume that a `jmp_buf' begins with a `__jmp_buf' and that
-       `__mask_was_saved' follows it.  Do not move these members
-       or add others before it.  */
-    __jmp_buf __jmpbuf;		/* Calling environment.  */
-    int __mask_was_saved;	/* Saved the signal mask?  */
-    __sigset_t __saved_mask;	/* Saved signal mask.  */
-  };
-
+#include <bits/types/struct___jmp_buf_tag.h>
 
 typedef struct __jmp_buf_tag jmp_buf[1];
 

sysdeps/nptl/pthread.h

@@ -28,6 +28,7 @@
 #include <bits/wordsize.h>
 #include <bits/types/struct_timespec.h>
 #include <bits/types/__sigset_t.h>
+#include <bits/types/struct___jmp_buf_tag.h>
 
 
 /* Detach state.  */
@@ -730,8 +731,8 @@ extern void __pthread_unwind_next (__pthread_unwind_buf_t *__buf)
 #endif
 
 /* Function used in the macros.  */
-struct __jmp_buf_tag;
-extern int __sigsetjmp (struct __jmp_buf_tag *__env, int __savemask) __THROWNL;
+extern int __sigsetjmp (struct __jmp_buf_tag __env[1],
+			int __savemask) __THROWNL;
 
 
 /* Mutex handling.  */