start-stop-daemon: set fds to CLOEXEC instead of closing

Set file descriptors to CLOEXEC instead of closing them before exec,
similar to what we do in supervise-daemon.

Use the share cloexec_fds_from() helper for this.

closefrom() is no longer used so remove the test.

meson.build

@@ -195,9 +195,6 @@ if cc.compiles(malloc_attribute_test, name : 'malloc attribute with arguments')
   add_project_arguments('-DHAVE_MALLOC_EXTENDED_ATTRIBUTE', language: 'c')
 endif
 
-if cc.has_function('closefrom', prefix: '#define _GNU_SOURCE\n#include <unistd.h>')
-  add_project_arguments('-DHAVE_CLOSEFROM', language: 'c')
-endif
 if cc.has_function('close_range', prefix: '#define _GNU_SOURCE\n#include <unistd.h>')
   add_project_arguments('-DHAVE_CLOSE_RANGE', language: 'c')
 endif

src/start-stop-daemon/start-stop-daemon.c

@@ -1098,12 +1098,7 @@ int main(int argc, char **argv)
 				|| rc_yesno(getenv("EINFO_QUIET")))
 			dup2(stderr_fd, STDERR_FILENO);
 
-#ifdef HAVE_CLOSEFROM
-		closefrom(3);
-#else
-		for (i = getdtablesize() - 1; i >= 3; --i)
-			close(i);
-#endif
+		cloexec_fds_from(3);
 
 		if (scheduler != NULL) {
 			int scheduler_index;