tests/attrtest: move decl to non-test file

Solves the asmdecl error:

  [amd64] AttrTest: function AttrTest missing Go declaration

Updates #24

tests/textflag/make_attrtest.go

@@ -44,7 +44,7 @@ func PrintAttributesTest(w io.Writer, as []attr.Attribute) {
 	_, self, _, _ := runtime.Caller(0)
 	fmt.Fprintf(w, "// Code generated by %s. DO NOT EDIT.\n\n", filepath.Base(self))
 	fmt.Fprintf(w, "#include \"textflag.h\"\n\n")
-	fmt.Fprintf(w, "TEXT ·AttrTest(SB), $0-1\n")
+	fmt.Fprintf(w, "TEXT ·attrtest(SB), $0-1\n")
 	fmt.Fprintf(w, "\tMOVB $0, ret+0(FP)\n")
 
 	for i, a := range as {