Fix .asciz <expr>... where an overzealous parsing wants to parse too much of the remaining text

In particular, the example was
	.asciz <cr><lf>/<SOH>/
where it tried to make a division betweem <lf> and the delimited
string /<SOH>/.

parse.h

@@ -35,6 +35,9 @@ int             get_mode(
 EX_TREE        *parse_expr(
     char *cp,
     int undef);
+EX_TREE        *parse_unary_expr(
+    char *cp,
+    int undef);
 int             parse_float(
     char *cp,
     char **endp,