Avoid interleaving stderr in a few cases

* src/sysdep.c (buferr): New static var.
(init_standard_fds) [_PC_PIPE_BUF]: Initialize it.
(errstream, errputc, verrprintf, errwrite): New functions.
(close_output_streams): Check buferr status too.
* src/xdisp.c: Include sysstdio.h instead of stdio.h.
(message_to_stderr, vmessage): Use the new functions
to avoid interleaving stderr.

1 files changed, 3 insertions, 0 deletions

diff --git a/src/sysstdio.h b/src/sysstdio.h
index 68ae043fe33..5303e8a15b2 100644
--- a/src/sysstdio.h
+++ b/src/sysstdio.h
@@ -25,6 +25,9 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 #include "unlocked-io.h"
 
 extern FILE *emacs_fopen (char const *, char const *);
+extern void errputc (int);
+extern void verrprintf (char const *, va_list) ATTRIBUTE_FORMAT_PRINTF (1, 0);
+extern void errwrite (void const *, ptrdiff_t);
 extern void close_output_streams (void);
 
 #if O_BINARY