[clang] [llvm] Remove Native Client support (PR #133661)

[Fangrui Song via cfe-commits]

MaskRay wrote:

> Thanks for working on this! This will be the first time I'm not going to oppose an effort to remove Native Client support 🎉 Although I am going to ask you to wait a couple of months to land it, until we finally turn it off for good and start deleting the support code from Chromium. This is planned after the M139 branch in late June. I will also give this a good review.

Is it feasible to remove ARM and MIPS support earlier? (Also make the PR smaller)

> @MaskRay Another thing I wanted to ask about was there were some tests I removed with nacl in the name that used nacl triples as well as rodata-section.s. I am not sure if any of them are still relevant outside of a nacl environment. Should they be renamed and use a different triple or any other changes?

`test/MC/X86/AlignedBundling` is for an assembler extension only used by nacl. Should be fine to remove `test/MC/X86/AlignedBundling/rodata-section.s`

https://github.com/llvm/llvm-project/pull/133661