benchmark: separate RegExp benchmark from v8 basic bench

[yosuke-furukawa]

RegExp bench is separated from run.js. And I created runRegExp.js for running another contexts.

RegExp bench creates global RegExp (https://github.com/iojs/io.js/blob/v1.x/deps/v8/benchmarks/regexp.js#L40).
However, the RegExp causes a error. The detail is here.

#475

[bnoordhuis]

Thanks for bringing that up, @yosuke-furukawa. I suggested an alternative approach in #489 (and I'd like you to review it, if you don't mind) because I'd rather not touch files in the deps/ directory.

[cjihrig]

Closing in favor of #489 since @yosuke-furukawa LGTM'ed it.