Auto merge of #125930 - weihanglo:opt-dist-respect-cargo-config, r=<try>

feat(opt-dist): respect existing .cargo/config.toml

This should be the last piece toward self-contained `opt-dist` (I believe).

It fixes the issue described in #125465

> * The current pinned rustc-perf uses `tempfile::Tempdir` as the working
  directory when collecting profiles from some of these packages.
  This "tmp" working directory usage make it impossible for Cargo to pick
  up the correct vendor sources setting in `.cargo/config.toml` bundled
  in the rustc-src tarball. [^1]
> [^1]: https://github.com/rust-lang/rustc-perf/blob/4f313add609f43e928e98132358e8426ed3969ae/collector/src/compile/benchmark/mod.rs#L164-L173

See also

* <rust-lang/rustc-perf#1913>
* <#125465>
* https://rust-lang.zulipchat.com/#narrow/stream/247081-t-compiler.2Fperformance/topic/tempfile.20in.20rustc-perf.20make.20it.20hard.20to.20configure.20vendor

r​? Kobzol

Author: bors

src/tools/opt-dist/src/training.rs

@@ -36,7 +36,7 @@ fn init_compiler_benchmarks(
     // Run rustc-perf benchmarks
     // Benchmark using profile_local with eprintln, which essentially just means
     // don't actually benchmark -- just make sure we run rustc a bunch of times.
-    cmd(&[
+    let mut cmd = cmd(&[
         env.cargo_stage_0().as_str(),
         "run",
         "-p",
@@ -61,7 +61,16 @@ fn init_compiler_benchmarks(
     .env("RUST_LOG", "collector=debug")
     .env("RUSTC", env.rustc_stage_0().as_str())
     .env("RUSTC_BOOTSTRAP", "1")
-    .workdir(&env.rustc_perf_dir())
+    .workdir(&env.rustc_perf_dir());
+
+    // Respect `.cargo/config.toml` in the rustc source. This is useful when the
+    // source is from a tarball and contains vendored source settings.
+    let dot_cargo_config_toml = env.checkout_path().join(".cargo").join("config.toml");
+    if dot_cargo_config_toml.is_file() {
+        cmd = cmd.arg("--cargo-config").arg(dot_cargo_config_toml);
+    }
+
+    cmd
 }
 
 /// Describes which `llvm-profdata` binary should be used for merging PGO profiles.