hir: Don't allocate for intrinsic inputs

This isn't exactly a hot path, but it does allocate for data with a
statically known length. `arrayvec` is already in the crate graph, so
use it here to avoid any allocation.

Author: tgross35

Cargo.lock

@@ -3740,6 +3740,7 @@ dependencies = [
 name = "rustc_hir_analysis"
 version = "0.0.0"
 dependencies = [
+ "arrayvec",
  "itertools",
  "rustc_abi",
  "rustc_arena",

compiler/rustc_hir_analysis/Cargo.toml

@@ -9,6 +9,7 @@ doctest = false
 
 [dependencies]
 # tidy-alphabetical-start
+arrayvec = { version = "0.7", default-features = false }
 itertools = "0.12"
 rustc_abi = { path = "../rustc_abi" }
 rustc_arena = { path = "../rustc_arena" }