Add a test for function accumulation attribute

tests/accumulate.qc

@@ -0,0 +1,15 @@
+void foo() {
+    print("hello ");
+}
+
+[[accumulate]] void foo() {
+    print("accumulation ");
+}
+
+[[accumulate]] void foo() {
+    print("world\n");
+}
+
+void main() {
+    foo();
+}

tests/accumulate.tmpl

@@ -0,0 +1,5 @@
+I: accumulate.qc
+D: test function accumulation
+T: -execute
+C: -std=gmqcc
+M: hello accumulation world