runtime: `build.sh` fails when run in a directory that contains spaces

Building with spaces seems to fail about once a year. Which tells me that the developers working on this day to day just avoid it and it will keep breaking periodically unless we make CI work this way.

We could just document that we don’t support it…

There could be some weekly CI job that’d build and test from a directory that contains spaces and non-ASCII characters, this’d keep things working in check.

Sure, we all strive to avoid it, but some people are less lucky - in many institutions, universities, companies, IT may force a policy that requires people to use root folders with names beyond their control (e.g. based on their names that may contain a plethora of accent signs and spaces). While it’s a sad reality that today this doesn’t work, I think our north star should be ultimately making this fully functional, at the very least as a nod to our inclusiveness principle.