main: add interp tests

This one needed more advanced checking of the error messages, because we
don't want to hardcode things like `!dbg !10` in the output.

testdata/errors/interp.go

@@ -0,0 +1,31 @@
+package main
+
+import _ "unsafe"
+
+func init() {
+	foo()
+}
+
+func foo() {
+	interp_test_error()
+}
+
+// This is a function that always causes an error in interp, for testing.
+//
+//go:linkname interp_test_error __tinygo_interp_raise_test_error
+func interp_test_error()
+
+func main() {
+}
+
+// ERROR: # main
+// ERROR: {{.*testdata[\\/]errors[\\/]interp\.go}}:10:19: test error
+// ERROR:   call void @__tinygo_interp_raise_test_error{{.*}}
+// ERROR: {{}}
+// ERROR: traceback:
+// ERROR: {{.*testdata[\\/]errors[\\/]interp\.go}}:10:19:
+// ERROR:   call void @__tinygo_interp_raise_test_error{{.*}}
+// ERROR: {{.*testdata[\\/]errors[\\/]interp\.go}}:6:5:
+// ERROR:   call void @main.foo{{.*}}
+// ERROR: {{.*testdata[\\/]errors}}:
+// ERROR:   call void @"main.init#1"{{.*}}