message: Remove all `CARGO_*` env vars in tests
  Usage of `CARGO_PROFILE_*` is generating unexpected warnings in tests in
  rust-lang/rust#64316 so let's just blanket remove every env var that has
  a `CARGO_*` prefix which generally means Cargo-specific env vars. Tests
  practically all assume that they have blank configs right now.
diff: @@ -1694,8 +1694,17 @@ pub fn process<T: AsRef<OsStr>>(t: T) -> cargo::util::ProcessBuilder {
  fn _process(t: &OsStr) -> cargo::util::ProcessBuilder {
  let mut p = cargo::util::process(t);
  +
  + // In general just clear out all cargo-specific configuration already in the
  + // environment. Our tests all assume a "default configuration" unless
  + // specified otherwise.
  + for (k, _v) in env::vars() {
  + if k.starts_with("CARGO_") {
  + p.env_remove(&k);
  + }
  + }
  +
  p.cwd(&paths::root())
  - .env_remove("CARGO_HOME")
  .env("HOME", paths::home())
  .env("CARGO_HOME", paths::home().join(".cargo"))
  .env("__CARGO_TEST_ROOT", paths::root())
  @@ -1707,10 +1716,6 @@ fn _process(t: &OsStr) -> cargo::util::ProcessBuilder {
  // stable channel yet. Once incremental support hits the stable compiler we
  // can switch this to one and then fix the tests.
  .env("CARGO_INCREMENTAL", "0")
  - // This env var can switch the git backend from libgit2 to git2-curl, which
  - // can tweak error messages and cause some tests to fail, so let's forcibly
  - // remove it.
  - .env_remove("CARGO_HTTP_CHECK_REVOKE")
  .env_remove("__CARGO_DEFAULT_LIB_METADATA")
  .env_remove("RUSTC")
  .env_remove("RUSTDOC")
  @@ -1722,12 +1727,10 @@ fn _process(t: &OsStr) -> cargo::util::ProcessBuilder {
  .env_remove("USER") // not set on some rust-lang docker images
  .env_remove("MFLAGS")
  .env_remove("MAKEFLAGS")
  - .env_remove("CARGO_MAKEFLAGS")
  .env_remove("GIT_AUTHOR_NAME")
  .env_remove("GIT_AUTHOR_EMAIL")
  .env_remove("GIT_COMMITTER_NAME")
  .env_remove("GIT_COMMITTER_EMAIL")
  - .env_remove("CARGO_TARGET_DIR") // we assume 'target'
  .env_remove("MSYSTEM"); // assume cmd.exe everywhere on windows
  p
  }
  