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 *
Instead of having a special case in the dynamic loader where we ignore
TM-related GCC symbols, just stub them out in LibC like we already do
for various other things we don't support.