microsoft/compiler: Truncate function names when needed

microsoft/compiler: Truncate function names when needed

DXIL metadata strings and function names have a limited size. Truncate
the name when they don't fit. This is a quick&dirty workaround since it
doesn't address the problem for all kind of strings, and doesn't ensure
there's no collision in the function names after the truncation. That's
not an issue right now because I don't think we have implementations
keeping more than one function (the entrypoint), but it might be a
problem at some point.

Acked-by: Jesse Natalie <jenatali@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16961>