rustc_driver: get rid of extra thread on Windows

src/librustc_driver/lib.rs

@@ -1488,7 +1488,11 @@ pub fn in_rustc_thread<F, R>(f: F) -> Result<R, Box<Any + Send>>
         }
     };
 
-    #[cfg(not(unix))]
+    // We set the stack size at link time. See src/rustc/rustc.rs.
+    #[cfg(windows)]
+    let spawn_thread = false;
+
+    #[cfg(not(any(windows,unix)))]
     let spawn_thread = true;
 
     // The or condition is added from backward compatibility.

src/rustc/rustc.rs

@@ -9,6 +9,15 @@
 // except according to those terms.
 
 #![feature(rustc_private)]
+#![feature(link_args)]
+
+// Set the stack size at link time on Windows. See rustc_driver::in_rustc_thread
+// for the rationale.
+#[cfg_attr(all(windows, target_env = "msvc"), link_args = "/STACK:16777216")]
+// We only build for msvc and gnu now, but we use a exhaustive condition here
+// so we can expect either the stack size to be set or the build fails.
+#[cfg_attr(all(windows, not(target_env = "msvc")), link_args = "-Wl,--stack,16777216")]
+extern {}
 
 extern crate rustc_driver;