Auto merge of #122362 - Zoxc:rustc_driver_static_std, r=oli-obk,lqd,bjorn3,Kobzol

Link `std` statically in `rustc_driver`

This makes `rustc_driver` statically link to `std`. This is done by not passing `-C prefer-dynamic` when building `rustc_driver`. However building `rustc-main` won't work currently as it tries to dynamically link to both `rustc_driver` and `std` resulting in a crate graph with `std` duplicated. To fix that new command line option `-Z prefer_deps_of_dynamic` is added which prevents linking to a dylib if there's a static variant of it already statically linked into another dylib dependency.

The main motivation for this change is to enable `#[global_allocator]` to be used in `rustc_driver` allowing overriding the allocator used in rustc on all platforms.

---

Instead of adding `-Z prefer_deps_of_dynamic`, this PR is changed to crate opt-in to the linking change via the `rustc_private` feature instead, as that would be typically needed to link to `rustc_driver` anyway.

---

try-job: aarch64-apple
try-job: x86_64-msvc
try-job: i686-mingw
try-job: dist-x86_64-msvc
try-job: aarch64-gnu

4 files changed, 13 insertions, 0 deletions

diff --git a/src/tools/clippy/src/main.rs b/src/tools/clippy/src/main.rs
index c9af2138a72..c9853e53f3b 100644
--- a/src/tools/clippy/src/main.rs
+++ b/src/tools/clippy/src/main.rs
@@ -1,3 +1,6 @@
+// We need this feature as it changes `dylib` linking behavior and allows us to link to
+// `rustc_driver`.
+#![feature(rustc_private)]
 // warn on lints, that are included in `rust-lang/rust`s bootstrap
 #![warn(rust_2018_idioms, unused_lifetimes)]
 
diff --git a/src/tools/clippy/tests/compile-test.rs b/src/tools/clippy/tests/compile-test.rs
index c7080e5dcdc..64253514fbe 100644
--- a/src/tools/clippy/tests/compile-test.rs
+++ b/src/tools/clippy/tests/compile-test.rs
@@ -1,3 +1,6 @@
+// We need this feature as it changes `dylib` linking behavior and allows us to link to
+// `rustc_driver`.
+#![feature(rustc_private)]
 #![warn(rust_2018_idioms, unused_lifetimes)]
 #![allow(unused_extern_crates)]
 
diff --git a/src/tools/rustdoc/main.rs b/src/tools/rustdoc/main.rs
index 5b499a1fa1f..d4099cafe5d 100644
--- a/src/tools/rustdoc/main.rs
+++ b/src/tools/rustdoc/main.rs
@@ -1,3 +1,6 @@
+// We need this feature as it changes `dylib` linking behavior and allows us to link to `rustc_driver`.
+#![feature(rustc_private)]
+
 fn main() {
     rustdoc::main()
 }
diff --git a/src/tools/rustfmt/src/git-rustfmt/main.rs b/src/tools/rustfmt/src/git-rustfmt/main.rs
index 3059d917c6b..5674f40bef9 100644
--- a/src/tools/rustfmt/src/git-rustfmt/main.rs
+++ b/src/tools/rustfmt/src/git-rustfmt/main.rs
@@ -1,3 +1,7 @@
+// We need this feature as it changes `dylib` linking behavior and allows us to link to
+// `rustc_driver`.
+#![feature(rustc_private)]
+
 #[macro_use]
 extern crate tracing;