Compile-time If Bugfix

Oops, fixed a bug where the first branch of an #if had scoping issues where the declarations were not correctly placed at the top-level scope.

Also, there are obvious security implications for being able to #run arbitrary code at compile-time, eg. #run system("rm -rf /*") (thanks, sim642), especially from an imported library.

We'll probably disable calling out to external functions during compile time, or have some way to change that (flag, or directive on imports, or something).