supervise-daemon: rename HAVE_CLOSE_RANGE_EXEC to HAVE_CLOSE_RANGE

Use HAVE_CLOSE_RANGE to tell if system provides a close_range(2)
wrapper, which better explains the purpose.

Add a compat inline which returns -1 if close_range is unavailable.

meson.build

@@ -200,7 +200,7 @@ if cc.has_function('closefrom', prefix: '#define _GNU_SOURCE\n#include <unistd.h
 endif
 if cc.has_function('close_range', prefix: '#define _GNU_SOURCE\n#include <unistd.h>') and \
     cc.has_header_symbol('unistd.h', 'CLOSE_RANGE_CLOEXEC', prefix: '#define _GNU_SOURCE')
-  add_project_arguments('-DHAVE_CLOSE_RANGE_CLOEXEC', language: 'c')
+  add_project_arguments('-DHAVE_CLOSE_RANGE', language: 'c')
 endif
 
 if cc.has_function('strlcpy', prefix: '#define _GNU_SOURCE\n#include <string.h>')

src/supervise-daemon/supervise-daemon.c

@@ -22,7 +22,7 @@
 #define ONE_SECOND    1000000000
 #define ONE_MS           1000000
 
-#ifdef HAVE_CLOSE_RANGE_CLOEXEC
+#ifdef HAVE_CLOSE_RANGE
 /* For close_range() */
 # define _GNU_SOURCE
 #endif
@@ -203,6 +203,18 @@ static inline int ioprio_set(int which RC_UNUSED, int who RC_UNUSED,
 }
 #endif
 
+#ifndef CLOSE_RANGE_CLOEXEC
+# define CLOSE_RANGE_CLOEXEC	(1U << 2)
+#endif
+#ifndef HAVE_CLOSE_RANGE
+static inline int close_range(unsigned int first RC_UNUSED,
+			      unsigned int last RC_UNUSED,
+			      unsigned int flags RC_UNUSED)
+{
+	return -1;
+}
+#endif
+
 static void cleanup(void)
 {
 	free(changeuser);
@@ -570,9 +582,7 @@ RC_NORETURN static void child_process(char *exec, char **argv)
 	if (redirect_stderr || rc_yesno(getenv("EINFO_QUIET")))
 		dup2(stderr_fd, STDERR_FILENO);
 
-#ifdef HAVE_CLOSE_RANGE_CLOEXEC
 	if (close_range(3, UINT_MAX, CLOSE_RANGE_CLOEXEC) < 0)
-#endif
 		for (i = getdtablesize() - 1; i >= 3; --i)
 			fcntl(i, F_SETFD, FD_CLOEXEC);
 	cmdline = make_cmdline(argv);