Only strip librustc_driver and libLLVM during x dist

The strip invocation can be quite slow (~1-2 seconds), and it is executed on every compiler bootstrap refresh when debuginfo is turned off, which can make most bootstrap commands quite slow.

Author: Kobzol

src/bootstrap/src/core/build_steps/compile.rs

@@ -2143,6 +2143,12 @@ pub enum CargoMessage<'a> {
 }
 
 pub fn strip_debug(builder: &Builder<'_>, target: TargetSelection, path: &Path) {
+    // Only perform stripping in dist builds, to save time (strip can be slow) during local
+    // development.
+    if builder.kind != Kind::Dist {
+        return;
+    }
+
     // FIXME: to make things simpler for now, limit this to the host and target where we know
     // `strip -g` is both available and will fix the issue, i.e. on a x64 linux host that is not
     // cross-compiling. Expand this to other appropriate targets in the future.