SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
I originally wanted to batch the symbolication requests but that just
makes the client logic significantly more complicated with no real
benefit other than architectural feelgood points.
Since this is useful in many places, let's have a common implementation
of walking the stack of a given thread via /proc and symbolicating each
of the frames.
