util/ulockmgr_server.c: conditionally define closefrom (fix glibc-2.34+)

closefrom(3) has joined us in glibc-land from *BSD and Solaris. Since
it's available in glibc 2.34+, we want to detect it and only define our
fallback if the libc doesn't provide it.

Bug: https://bugs.gentoo.org/803923
Signed-off-by: Sam James <sam@gentoo.org>

configure.ac

@@ -55,6 +55,7 @@ fi
 
 AC_CHECK_FUNCS([fork setxattr fdatasync splice vmsplice utimensat])
 AC_CHECK_FUNCS([posix_fallocate])
+AC_CHECK_FUNCS([closefrom])
 AC_CHECK_MEMBERS([struct stat.st_atim])
 AC_CHECK_MEMBERS([struct stat.st_atimespec])
 

util/ulockmgr_server.c

@@ -22,6 +22,10 @@
 #include <sys/socket.h>
 #include <sys/wait.h>
 
+#ifdef HAVE_CONFIG_H
+	#include "config.h"
+#endif
+
 struct message {
 	unsigned intr : 1;
 	unsigned nofd : 1;
@@ -124,6 +128,7 @@ static int receive_message(int sock, void *buf, size_t buflen, int *fdp,
 	return res;
 }
 
+#if !defined(HAVE_CLOSEFROM)
 static int closefrom(int minfd)
 {
 	DIR *dir = opendir("/proc/self/fd");
@@ -141,6 +146,7 @@ static int closefrom(int minfd)
 	}
 	return 0;
 }
+#endif
 
 static void send_reply(int cfd, struct message *msg)
 {