> It's not really a perf problem, just a nice to have, think it's worth adding this (minor) complexity?

I guess the answer depends on whether we can expect to get rid of the `stage0` case.

Although I actually question whether we even need it. `make check-stage0-cfail` tells me 

    make: *** No rule to make target `x86_64-apple-darwin/stage0/bin/compiletest', needed by `tmp/check-stage0-T-x86_64-apple-darwin-H-x86_64-apple-darwin-cfail.ok'.  Stop

It appears the first compiletest I can build is the stage1 compiletest. It's built using the stage0 `rustc`, but I don't see why we can't ask the build system to compile the `regex_macros` crate.

That said, since it's probably more complicated than a 1-line change, it may make more sense just to stick with the dynamic approach. Of course this approach is unnecessarily recompiling the regex for every file, but I don't know if that performance hit is noticeable.