Use of undeclared Var cljs.user/RegExp when extending protocol for RegExp
Description
WARNING: Use of undeclared Var schema.core/RegExp at line 356 /home/juho/.boot/cache/tmp/home/juho/Source/**/**/4i8/-uc8bn7/js/main.out/schema/core.cljs WARNING: Use of undeclared Var bidi.bidi/RegExp at line 232 /home/juho/.boot/cache/tmp/home/juho/Source/**/**/4i8/-uc8bn7/js/main.out/bidi/bidi.cljc
WARNING: Use of undeclared Var schema.core/RegExp at line 356 /home/juho/.boot/cache/tmp/home/juho/Source/**/**/4i8/-uc8bn7/js/main.out/schema/core.cljs
WARNING: Use of undeclared Var bidi.bidi/RegExp at line 232 /home/juho/.boot/cache/tmp/home/juho/Source/**/**/4i8/-uc8bn7/js/main.out/bidi/bidi.cljc
https://github.com/juxt/bidi/blob/master/src/bidi/bidi.cljc#L230
https://github.com/plumatic/schema/blob/master/src/cljx/schema/core.cljx#L355
First commit with problem: https://github.com/clojure/clojurescript/commit/d961e66edfd3d62f80bed18418c597ee1f569e85
Test case by thheller: