starter: Don't directly refer to source files in Makefile for unit tests

Older versions of automake have trouble recursively cleaning such
constructs properly.

src/starter/tests/Makefile.am

@@ -4,9 +4,6 @@ check_PROGRAMS = $(TESTS)
 
 starter_tests_SOURCES = \
 	suites/test_parser.c \
-	../parser/conf_parser.c \
-	../parser/lexer.l \
-	../parser/parser.y \
 	starter_tests.h starter_tests.c
 
 starter_tests_CFLAGS = \
@@ -18,4 +15,5 @@ starter_tests_CFLAGS = \
 starter_tests_LDFLAGS = @COVERAGE_LDFLAGS@
 starter_tests_LDADD = \
 	$(top_builddir)/src/libstrongswan/libstrongswan.la \
-	$(top_builddir)/src/libstrongswan/tests/libtest.la
+	$(top_builddir)/src/libstrongswan/tests/libtest.la \
+	../libstarter.la