Remove all functions with platform #if's from fenv, and
add arch dependent implementations instead. The build
system now selects the implementation based on the platform.
Even though this almost certainly wouldn't run properly even if we had
a working kernel for AARCH64 this at least lets us build all the
userland binaries.
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 *
