_ prefixed top-level symbols now file-local

examples/packages/hidden_invalid/app/a.bro

@@ -0,0 +1,13 @@
+_sibling func() i32 {
+	return 1
+}
+
+_Sibling :: struct {
+	value i32
+}
+
+_sibling_value :: 1
+
+_collision c_func() i32 {
+	return 1
+}

examples/packages/hidden_invalid/app/b.bro

@@ -0,0 +1,17 @@
+import "../dep"
+
+_collision func() i32 {
+	return 2
+}
+
+read_sibling func(value _Sibling) i32 {
+	return value.value + _sibling_value
+}
+
+read_sibling_value func() i32 {
+	return _sibling_value
+}
+
+main func() i32 {
+	return _sibling() + dep._secret() + read_sibling(_Sibling { value = 1 }) + read_sibling_value()
+}