Make some linux/unix APIs better conform to strict provenance.

This largely makes the stdlib conform to strict provenance on Ubuntu.
Some hairier things have been left alone for now.

library/std/src/backtrace.rs

@@ -493,7 +493,7 @@ impl RawFrame {
         match self {
             RawFrame::Actual(frame) => frame.ip(),
             #[cfg(test)]
-            RawFrame::Fake => ptr::invalid_mut(1),
+            RawFrame::Fake => crate::ptr::invalid_mut(1),
         }
     }
 }