[dev.cc] cmd/asm: accept #define A /* nothing */

Was rejected but should be legal.

Change-Id: I0189e3bef6b67c6ba390c75a48a8d9d8f39b7636
Reviewed-on: https://go-review.googlesource.com/5286Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/asm/internal/lex/input.go

@@ -206,7 +206,7 @@ func (in *Input) macroDefinition(name string) ([]string, []Token) {
 	prevCol := in.Stack.Col()
 	tok := in.Stack.Next()
 	if tok == '\n' || tok == scanner.EOF {
-		in.Error("no definition for macro:", name)
+		return nil, nil // No definition for macro
 	}
 	var args []string
 	// The C preprocessor treats

src/cmd/asm/internal/lex/lex_test.go

@@ -36,6 +36,11 @@ var lexTests = []lexTest{
 		),
 		"1234.\n",
 	},
+	{
+		"define without value",
+		"#define A",
+		"",
+	},
 	{
 		"macro without arguments",
 		"#define A() 1234\n" + "A()\n",