--- a/ChangeLog	Sun Feb 04 11:00:38 2018 +0100
+++ b/ChangeLog	Sat Feb 17 09:55:43 2018 +0100
@@ -1,3 +1,11 @@
+2018-02-17  Bruno Haible  <bruno@clisp.org>
+
+	thread: Fix compilation error on IRIX.
+	* lib/glthread/thread.h: Include <unistd.h>. Include <signal.h> when
+	needed; include it outside the C++ extern "C" {} block.
+	* doc/posix-headers/pthread.texi: Mention the problem with
+	pthread_atfork on IRIX.
+
 2018-02-04  Bruno Haible  <bruno@clisp.org>
 
 	nl_langinfo: Override the system's nl_langinfo() when needed.

--- a/doc/posix-headers/pthread.texi	Sun Feb 04 11:00:38 2018 +0100
+++ b/doc/posix-headers/pthread.texi	Sat Feb 17 09:55:43 2018 +0100
@@ -21,4 +21,8 @@
 not offer threads, so much as lightweight stubs that make conditional
 compilation easier for fallbacks to single-threaded programs.
 Minix 3.1.8, mingw 2.x, MSVC 14, BeOS.
+@item
+This header file lacks the declaration of @code{pthread_atfork} on some
+platforms:
+IRIX 6.5.
 @end itemize

--- a/lib/glthread/thread.h	Sun Feb 04 11:00:38 2018 +0100
+++ b/lib/glthread/thread.h	Sat Feb 17 09:55:43 2018 +0100
@@ -90,6 +90,17 @@
 
 # include <pthread.h>
 
+/* On IRIX, pthread_atfork is declared in <unistd.h>, not in <pthread.h>.  */
+# if defined __sgi
+#  include <unistd.h>
+# endif
+
+# if USE_POSIX_THREADS_WEAK
+/* Compilers other than GCC need to see the declaration of pthread_sigmask
+   before the "#pragma weak pthread_sigmask" below.  */
+#  include <signal.h>
+# endif
+
 # ifdef __cplusplus
 extern "C" {
 # endif
@@ -124,10 +135,6 @@
 
 #  pragma weak pthread_create
 
-#  ifdef __clang__
-  /* Without this, clang complains that pthread_sigmask is never declared.  */
-#   include <signal.h>
-#  endif
 #  ifndef pthread_sigmask /* Do not declare rpl_pthread_sigmask weak.  */
 #   pragma weak pthread_sigmask
 #  endif