Follow autoconf recommendation for TESTSUITEFLAGS.

* tests/Makefile.am (check-local, installcheck-local): Honor
TESTSUITEFLAGS.

tests/Makefile.am

@@ -140,7 +140,7 @@ clean-local:
 	test ! -f $(TESTSUITE) || $(SHELL) $(TESTSUITE) --clean
 
 check-local: atconfig atlocal $(TESTSUITE)
-	$(SHELL) $(TESTSUITE)
+	$(SHELL) $(TESTSUITE) $(TESTSUITEFLAGS)
 
 check-full:
 	FULL_TEST=1 $(MAKE) check
@@ -149,7 +149,7 @@ check-full:
 
 # Run the test suite on the *installed* tree.
 installcheck-local:
-	$(SHELL) $(TESTSUITE) AUTOTEST_PATH=$(exec_prefix)/bin
+	$(SHELL) $(TESTSUITE) $(TESTSUITEFLAGS) AUTOTEST_PATH=$(exec_prefix)/bin
 
 
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