Auto merge of #36441 - alexcrichton:rustbuild-target, r=brson

rustbuild: Fix cross-compiles to MinGW on Linux

Closes #36290
Closes #36291

Author: bors

src/bootstrap/compile.rs

@@ -128,14 +128,16 @@ fn build_startup_objects(build: &Build, target: &str, into: &Path) {
         return
     }
     let compiler = Compiler::new(0, &build.config.build);
-    let compiler = build.compiler_path(&compiler);
+    let compiler_path = build.compiler_path(&compiler);
 
     for file in t!(fs::read_dir(build.src.join("src/rtstartup"))) {
         let file = t!(file);
-        build.run(Command::new(&compiler)
-                          .arg("--emit=obj")
-                          .arg("--out-dir").arg(into)
-                          .arg(file.path()));
+        let mut cmd = Command::new(&compiler_path);
+        build.add_bootstrap_key(&compiler, &mut cmd);
+        build.run(cmd.arg("--target").arg(target)
+                     .arg("--emit=obj")
+                     .arg("--out-dir").arg(into)
+                     .arg(file.path()));
     }
 
     for obj in ["crt2.o", "dllcrt2.o"].iter() {

src/rtstartup/rsbegin.rs

@@ -22,10 +22,19 @@
 // object (usually called `crtX.o), which then invokes initialization callbacks
 // of other runtime components (registered via yet another special image section).
 
+#![feature(no_core, lang_items)]
 #![crate_type="rlib"]
-#![no_std]
+#![no_core]
 #![allow(non_camel_case_types)]
 
+#[lang = "sized"]
+trait Sized {}
+#[lang = "sync"]
+trait Sync {}
+#[lang = "copy"]
+trait Copy {}
+impl<T> Sync for T {}
+
 #[cfg(all(target_os="windows", target_arch = "x86", target_env="gnu"))]
 pub mod eh_frames {
     #[no_mangle]

src/rtstartup/rsend.rs

@@ -10,8 +10,15 @@
 
 // See rsbegin.rs for details.
 
+#![feature(no_core, lang_items)]
 #![crate_type="rlib"]
-#![no_std]
+#![no_core]
+
+#[lang = "sized"]
+trait Sized {}
+#[lang = "sync"]
+trait Sync {}
+impl<T> Sync for T {}
 
 #[cfg(all(target_os="windows", target_arch = "x86", target_env="gnu"))]
 pub mod eh_frames {

src/rustc/std_shim/Cargo.lock

@@ -41,6 +41,7 @@ debug-assertions = false
 
 [dependencies]
 std = { path = "../../libstd" }
+core = { path = "../../libcore" }
 
 # Reexport features from std
 [features]

src/rustc/std_shim/Cargo.toml

@@ -9,3 +9,9 @@
 // except according to those terms.
 
 // See comments in Cargo.toml for why this exists
+
+// There's a bug right now where if we pass --extern std=... and we're cross
+// compiling then this doesn't work with `#[macro_use] extern crate std;`. Work
+// around this by not having `#[macro_use] extern crate std;`
+#![no_std]
+extern crate std;