/*@cc_on!@*/
is not a regular expression, but a multi-line JavaScript comment (/* .. comment .. */
). In Internet Explorer, this is more than a comment. The code is parsed and evaluated (this feature is called conditional compilation).
The */
in your code ends the GWT-specific /*-{
section, causing the error to show up.
The solution is to use a different way to write down the comment:
var ie = false;
//@cc_on ie = true;
Another method, also safe against JavaScript minifiers is:
var ie = eval('/*@cc_on!@*'+'/false');