configure: make setbacklight optional

Modify the pkg-config check for setbacklight so that failure only
disables building setbacklight, instead of failing the whole configure.

Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>

tests/Makefile.am

@@ -22,7 +22,7 @@ event_test_la_SOURCES = event-test.c $(test_runner_src)
 test_client_SOURCES = test-client.c
 test_client_LDADD = $(SIMPLE_CLIENT_LIBS)
 
-noinst_PROGRAMS = setbacklight matrix-test
+noinst_PROGRAMS = $(setbacklight) matrix-test
 
 matrix_test_SOURCES =				\
 	matrix-test.c				\
@@ -38,4 +38,8 @@ setbacklight_SOURCES =				\
 setbacklight_CFLAGS = $(AM_CFLAGS) $(SETBACKLIGHT_CFLAGS)
 setbacklight_LDADD = $(SETBACKLIGHT_LIBS)
 
+if BUILD_SETBACKLIGHT
+setbacklight = setbacklight
+endif
+
 EXTRA_DIST = weston-test