syscalls/getdents: Add autotools check for getdents/getdents64

glibc 2.30 has added wrapper for getdents64, this will help in detecting
right condition to use fallback.

Check for getdents API as well while here.

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Petr Vorel <pvorel@suse.cz>
diff --git a/configure.ac b/configure.ac
index f7d1afc..5a882a3 100644
--- a/configure.ac
+++ b/configure.ac
@@ -69,6 +69,8 @@
     fallocate \
     fchownat \
     fstatat \
+    getdents \
+    getdents64 \
     kcmp \
     mkdirat \
     mknodat \