arm bswap32: fix fatal typo in thumb code (PR 55854)

arm bswap32: Improve the comments showing the byte flow.

It's confusing to use 1-4 for bytes 1-4 and then 0 for literal zero,
so use a-d for bytes 1-4.

Add thumb version
Use STRONG_ALIAS

Add some comments to illustrate what is actually happening.

Use the armv6 rev/rev16 if armv6 or later

Remove clause 3 and 4 from TNF licenses

Define htonl &co as alternative names to bswap only if little endian.
I'm not sure if idempotent versions need to be defined for big endian,
as the man page says in that case they are defined idempot

Define htonl &co as alternative names to bswap only if little endian.
I'm not sure if idempotent versions need to be defined for big endian,
as the man page says in that case they are defined idempotent macros.

PR port-arm/32734

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libc wants __bswapNN, kernel wants bswapNN. That was not accounted
for during the merge of kernel and libc versions. Fix to match
e.g. i386 code.

Merge libkern + libc common files. As requested by core.