Rollup merge of rust-lang#87358 - jyn514:dry-run, r=Mark-Simulacrum

Fix `--dry-run` when download-ci-llvm is set Previously it would error out: ``` $ x check --dry-run thread 'main' panicked at 'std::fs::read_to_string(ci_llvm.join("link-type.txt")) failed with No such file or directory (os error 2) ("CI llvm missing: /home/joshua/rustc3/build/tmp-dry-run/x86_64-unknown-linux-gnu/ci-llvm")', src/bootstrap/config.rs:795:33 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace Build completed unsuccessfully in 0:00:10 ```

Author: JohnTitor

src/bootstrap/config.rs

@@ -792,8 +792,16 @@ impl Config {
 
  // CI-built LLVM can be either dynamic or static.
  let ci_llvm = config.out.join(&*config.build.triple).join("ci-llvm");
- let link_type = t!(std::fs::read_to_string(ci_llvm.join("link-type.txt")));
- config.llvm_link_shared = link_type == "dynamic";
+ config.llvm_link_shared = if config.dry_run {
+ // just assume dynamic for now
+ true
+ } else {
+ let link_type = t!(
+ std::fs::read_to_string(ci_llvm.join("link-type.txt")),
+ format!("CI llvm missing: {}", ci_llvm.display())
+ );
+ link_type == "dynamic"
+ };
  }
 
  if config.llvm_thin_lto {