Link stage 2 tools dynamically to libstd

Author: smaeul

src/bootstrap/builder.rs

@@ -1838,7 +1838,7 @@ impl<'a> Builder<'a> {
         // When we build Rust dylibs they're all intended for intermediate
         // usage, so make sure we pass the -Cprefer-dynamic flag instead of
         // linking all deps statically into the dylib.
-        if matches!(mode, Mode::Std | Mode::Rustc) {
+        if matches!(mode, Mode::Std | Mode::Rustc | Mode::ToolRustc) {
             rustflags.arg("-Cprefer-dynamic");
         }