Auto-Generate Tables in platform-support.md

[qb42]

This is a rough draft inspired by @ChrisDenton in #150501 (comment). I won't have much time to work on it until next month but I wanted to get it out there.

This is implemented as an mdbook preprocessor that pulls data from the rustc_target crate, so it will always be accurate.

Assuming this works as intended (I am not set up to test locally), it's still missing the following:

• Links to target detail pages
• Footnotes

[Noratrieb]

This is very cool! I started a similar effort a while ago in #120745 but never got to completing it. Maybe some of the code in the linked PR thee may be useful

[qb42]

@Noratrieb Thanks, I'll take a look.

[qb42]

Alright, I'm set up properly now so no more failing tidy or pushing obvious mistakes.

Unfortunately it looks like depending on rustc_target directly is a dead-end, I'm getting a variety of errors related to it being a compiler-internal crate that is supposed to be compiled as part of bootstrap. The commit I just pushed (8c1125f) is my last attempt in that direction unless someone else has a solution.

I'm going to switch to pulling data from rustc -Z unstable-options --print all-target-specs-json and see how that goes.

[rust-log-analyzer]

The job aarch64-gnu-llvm-20-2 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

   Compiling memchr v2.7.6
error[E0725]: the feature `dropck_eyepatch` is not in the list of allowed features
  --> /cargo/registry/src/index.crates.io-1949cf8c6b5b557f/smallvec-1.15.1/src/lib.rs:96:45
   |
96 | #![cfg_attr(feature = "may_dangle", feature(dropck_eyepatch))]
   |                                             ^^^^^^^^^^^^^^^

For more information about this error, try `rustc --explain E0725`.
[RUSTC-TIMING] smallvec test:false 0.025
error: could not compile `smallvec` (lib) due to 1 previous error