configure.ac: check for sendfile

Do note that according to man sendfile, "Other UNIX systems implement
sendfile() with different semantics and prototypes."
If this is something we care about, a better check is needed.

Suggested-by: Karel Zak <kzak@redhat.com>
Reviewed-by: Sami Kerola <kerolasa@iki.fi>
Signed-off-by: Egor Chelak <egor.chelak@gmail.com>

configure.ac

@@ -530,6 +530,7 @@ AC_CHECK_FUNCS([ \
 	qsort_r \
 	rpmatch \
 	scandirat \
+	sendfile \
 	setprogname \
 	setresgid \
 	setresuid \

lib/fileutils.c

@@ -11,7 +11,9 @@
 #include <unistd.h>
 #include <sys/time.h>
 #include <sys/resource.h>
+#ifdef HAVE_SENDFILE
 #include <sys/sendfile.h>
+#endif
 #include <string.h>
 
 #include "c.h"
@@ -270,6 +272,7 @@ static int copy_file_simple(int from, int to)
 /* Copies the contents of a file. Returns -1 on read error, -2 on write error. */
 int ul_copy_file(int from, int to)
 {
+#ifdef HAVE_SENDFILE
 	struct stat st;
 	ssize_t nw;
 	off_t left;
@@ -290,4 +293,7 @@ int ul_copy_file(int from, int to)
 		if (nw < 0)
 			return copy_file_simple(from, to);
 	return 0;
+#else
+	return copy_file_simple(from, to);
+#endif
 }