patch 9.1.0842: not checking for the sync() systemcall

Problem:  not checking for the sync() systemcall
Solution: check for sync in configure script, fix related #ifdefs
          (Jonas Termansen)

It's better to check for features directly rather than maintaining a
denylist of operating systems without them.

closes: #15985

Signed-off-by: Jonas 'Sortie' Termansen <sortie@maxsi.org>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/auto/configure

@@ -13642,6 +13642,12 @@ then :
   printf "%s\n" "#define HAVE_CLOCK_GETTIME 1" >>confdefs.h
 
 fi
+ac_fn_c_check_func "$LINENO" "sync" "ac_cv_func_sync"
+if test "x$ac_cv_func_sync" = xyes
+then :
+  printf "%s\n" "#define HAVE_SYNC 1" >>confdefs.h
+
+fi
 
 
 

src/config.h.in

@@ -209,6 +209,7 @@
 #undef HAVE_CANBERRA
 #undef HAVE_SODIUM
 #undef HAVE_ST_BLKSIZE
+#undef HAVE_SYNC
 #undef HAVE_SYSCONF
 #undef HAVE_SYSCTL
 #undef HAVE_SYSINFO

src/configure.ac

@@ -3769,7 +3769,7 @@ AC_CHECK_FUNCS(fchdir fchown fchmod fsync getcwd getpseudotty \
 	sigprocmask sigvec strcasecmp strcoll strerror strftime stricmp strncasecmp \
 	strnicmp strpbrk strptime strtol tgetent towlower towupper iswupper \
 	tzset usleep utime utimes mblen ftruncate unsetenv posix_openpt \
-	clock_gettime)
+	clock_gettime sync)
 AC_FUNC_SELECT_ARGTYPES
 AC_FUNC_FSEEKO
 

src/memfile.c

@@ -594,13 +594,10 @@ mf_sync(memfile_T *mfp, int flags)
 	}
 	else
 # endif
-	    // OpenNT is strictly POSIX (Benzinger)
-	    // Tandem/Himalaya NSK-OSS doesn't have sync()
-	    // No sync() on Stratus VOS
-# if defined(__OPENNT) || defined(__TANDEM) || defined(__VOS__)
-	    fflush(NULL);
-# else
+# ifdef HAVE_SYNC
 	    sync();
+# else
+	    fflush(NULL);
 # endif
 #endif
 #ifdef VMS

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    842,
 /**/
     841,
 /**/