Upgrade to regalloc2 v0.2.2. (#4222)

Pulls in an improvement to spillslot allocation
(bytecodealliance/regalloc2#56).

Author: cfallin

Cargo.lock

@@ -23,7 +23,7 @@ serde = { version = "1.0.94", features = ["derive"], optional = true }
 bincode = { version = "1.2.1", optional = true }
 gimli = { version = "0.26.0", default-features = false, features = ["write"], optional = true }
 smallvec = { version = "1.6.1" }
-regalloc2 = { version = "0.2.1", features = ["checker"] }
+regalloc2 = { version = "0.2.2", features = ["checker"] }
 souper-ir = { version = "2.1.0", optional = true }
 # It is a goal of the cranelift-codegen crate to have minimal external dependencies.
 # Please don't add any unless they are essential to the task of creating binary