Recommend adding target spec first, then std support later

Co-Authored-By: Jieyou Xu <[email protected]>

Author: madsmtm

src/doc/rustc/src/target-tier-policy.md

@@ -125,6 +125,13 @@ To propose addition of a new target, open a pull request on [`rust-lang/rust`]:
 See also the documentation in the `rustc-dev-guide` on [adding a new target to
 `rustc`][rustc_dev_guide_add_target].
 
+Note that adding a new target that wants to support `std` would transitively
+require `cc` and `libc` support. However, these would like to know about the
+target from `rustc` as well. To break this cycle, you are strongly encouraged
+to add a _minimal_ `#![no_core]` target spec first to teach `rustc` about the
+target's existence, and add `std` support as a follow-up once you've added
+support for the target in `cc` and `libc`.
+
 [tier3example]: https://github.com/rust-lang/rust/pull/94872
 [platform_template]: https://github.com/rust-lang/rust/blob/master/src/doc/rustc/src/platform-support/TEMPLATE.md
 [summary]: https://github.com/rust-lang/rust/blob/master/src/doc/rustc/src/SUMMARY.md