Auto merge of #137198 - tgross35:cfg-match-rename, r=Amanieu

Rename `cfg_match!` to `cfg_select!`

[`@Nemo157` pointed out](rust-lang/rust#115585 (comment)) that `cfg_match!` syntax does not actually align well with match syntax, which is a possible source of confusion. The comment points out that usage is instead more similar to ecosystem `select!` macros. Rename `cfg_match!` to `cfg_select!` to match this.

Tracking issue: rust-lang/rust#115585

[1]: rust-lang/rust#115585 (comment)

Author: bors