signal: Fix a C++ compilation error due to sched_yield on OpenBSD 6.0

[Bruno Haible]

On OpenBSD 6.0, I'm seeing this compilation error:

depbase=`echo test-sched-c++.o | sed 's|[^/]*$|.deps/&|;s|\.o$||'`;\
g++ -DHAVE_CONFIG_H -DEXEEXT=\"\" -I. -I../../gltests -I..  
-DGNULIB_STRICT_CHECKING=1 -DIN_GNULIB_TESTS=1 -I. -I../../gltests -I.. 
-I../../gltests/.. -I../gllib -I../../gltests/../gllib -I/home/bruno/include 
-Wall  -Wno-error -g -O2 -MT test-sched-c++.o -MD -MP -MF $depbase.Tpo -c -o 
test-sched-c++.o ../../gltests/test-sched-c++.cc &&\
mv -f $depbase.Tpo $depbase.Po
In file included from /usr/include/pthread.h:47,
                 from ../gllib/pthread.h:46,
                 from ../gllib/signal.h:68,
                 from ../gllib/sys/select.h:119,
                 from /usr/include/sys/types.h:230,
                 from ../gllib/sys/types.h:39,
                 from /usr/include/sched.h:42,
                 from ../gllib/sched.h:30,
                 from ../../gltests/test-sched-c++.cc:22:
../gllib/sched.h: In member function 'gnulib::_gl_sched_yield_wrapper::operator 
int (*)()() const':
../gllib/sched.h:566: error: '::sched_yield' has not been declared
gmake[4]: *** [Makefile:23347: test-sched-c++.o] Error 1

The problem here is not that sched_yield is not declared, but rather that its
declaration comes too late, due to the sequence of #includes.

sched_yield is declared at /usr/include/sched.h:65
and used at gllib/sched.h:566.

test-sched-c++.cc:22 -> ../gllib/sched.h
../gllib/sched.h:30 -> /usr/include/sched.h
/usr/include/sched.h:42 -> ../gllib/sys/types.h
../gllib/sys/types.h:39 -> /usr/include/sys/types.h
/usr/include/sys/types.h:230 -> ../gllib/sys/select.h
../gllib/sys/select.h:119 -> ../gllib/signal.h            <-- HERE1
../gllib/signal.h:68 -> ../gllib/pthread.h                <-- HERE2
../gllib/pthread.h:46 -> /usr/include/pthread.h
/usr/include/pthread.h:47 -> ./gllib/sched.h
../gllib/sched.h:30 -> /usr/include/sched.h
                                     declares sched_yield

The natural places to cut down the #include forest is at HERE1 or HERE2.
And indeed the one at HERE2 is not needed any more in OpenBSD ≥ 5.1.
Thus, this patch fixes the issue.


2022-09-18  Bruno Haible  <bruno@clisp.org>

        signal: Fix a C++ compilation error due to sched_yield on OpenBSD 6.0.
        * lib/signal.in.h: On OpenBSD, include <sys/param.h>. Don't include
        <pthread.h> on OpenBSD ≥ 5.1.

diff --git a/lib/signal.in.h b/lib/signal.in.h
index 5d2d80c99d..c0d4848db0 100644
--- a/lib/signal.in.h
+++ b/lib/signal.in.h
@@ -55,12 +55,19 @@
 #ifndef _@GUARD_PREFIX@_SIGNAL_H
 #define _@GUARD_PREFIX@_SIGNAL_H
 
-/* Mac OS X 10.3, FreeBSD < 8.0, OpenBSD 3.8, OSF/1 4.0, Solaris 2.6, Android,
+/* For testing the OpenBSD version.  */
+#if (@GNULIB_PTHREAD_SIGMASK@ || defined GNULIB_POSIXCHECK) \
+    && defined __OpenBSD__
+# include <sys/param.h>
+#endif
+
+/* Mac OS X 10.3, FreeBSD < 8.0, OpenBSD < 5.1, OSF/1 4.0, Solaris 2.6, 
Android,
    OS/2 kLIBC declare pthread_sigmask in <pthread.h>, not in <signal.h>.
    But avoid namespace pollution on glibc systems.*/
 #if (@GNULIB_PTHREAD_SIGMASK@ || defined GNULIB_POSIXCHECK) \
     && ((defined __APPLE__ && defined __MACH__) \
-        || (defined __FreeBSD__ && __FreeBSD__ < 8) || defined __OpenBSD__ \
+        || (defined __FreeBSD__ && __FreeBSD__ < 8) \
+        || (defined __OpenBSD__ && OpenBSD < 201205) \
         || defined __osf__ || defined __sun || defined __ANDROID__ \
         || defined __KLIBC__) \
     && ! defined __GLIBC__