Allows our CI to catch more potential bugs. This also removes the
[[nodiscard]] attribute of IOFile's Open member function. There are
cases where a file may want to be opened, but have the status of it
checked at a later time.
Android and macOS have supported thread_local for quite a while, but
most importantly is that we don't even really need it. Instead of using
a thread-local buffer, we can just return a non-static buffer as a
std::string, avoiding the need for that quality entirely.
