Author: Helmut Grohne <helmut@subdivi.de>
Description: Fixes FTCBFS by not abusing AC_CHECK_FILE (Closes: #982523).

diff -Naurp netdata.orig/configure.ac netdata/configure.ac
--- netdata.orig/configure.ac
+++ netdata/configure.ac
@@ -1025,8 +1025,8 @@ if test "${build_target}" = "linux" -a "
         [#include <linux/bpf.h>]
     )
 
-    AC_CHECK_FILE(
-        externaldeps/libbpf/libbpf.a,
+    AS_IF(
+        [test -e externaldeps/libbpf/libbpf.a],
         [have_libbpf=yes],
         [have_libbpf=no]
     )