update -Cehcont-guard and comment

Author: sivadeilra

src/bootstrap/src/core/builder.rs

@@ -1964,10 +1964,14 @@ impl<'a> Builder<'a> {
             rustflags.arg("-Ccontrol-flow-guard");
         }
 
-        // Same for EHCont Guard (this is not combined with the previous if-statement to make
-        // merges with upstream easier).
+        // If EHCont Guard is enabled, pass the `-Zehcont-guard` flag to rustc when compiling the
+        // standard library, since this might be linked into the final outputs produced by rustc.
+        // Since this mitigation is only available on Windows, only enable it for the standard
+        // library in case the compiler is run on a non-Windows platform.
+        // This is not needed for stage 0 artifacts because these will only be used for building
+        // the stage 1 compiler.
         if cfg!(windows) && mode == Mode::Std && self.config.ehcont_guard && compiler.stage >= 1 {
-            rustflags.arg("-Cehcont-guard");
+            rustflags.arg("-Zehcont-guard");
         }
 
         // For `cargo doc` invocations, make rustdoc print the Rust version into the docs