tests: Use pkg-config to find setbacklight CFLAGS and libs
setbacklight depends on udev and drm, one cannot just add the -l flags
if you want to support unusual install paths.
diff --git a/configure.ac b/configure.ac
index c35d987..a8fc7f2 100644
--- a/configure.ac
+++ b/configure.ac
@@ -224,6 +224,7 @@
AC_CHECK_PROG(RSVG_CONVERT, rsvg-convert, rsvg-convert)
AM_CONDITIONAL(HAVE_RSVG_CONVERT, test -n "$RSVG_CONVERT")
+PKG_CHECK_MODULES(SETBACKLIGHT, [libudev libdrm])
if test "x$GCC" = "xyes"; then
my_common_gcc_flags="-Wall -Wextra -Wno-unused-parameter \