BacktraceStatus: add Eq impl

See discussion on rust-lang#53487.

Author: mathstuf

src/libstd/backtrace.rs

@@ -113,7 +113,7 @@ pub struct Backtrace {
 /// The current status of a backtrace, indicating whether it was captured or
 /// whether it is empty for some other reason.
 #[non_exhaustive]
-#[derive(Debug)]
+#[derive(Debug, PartialEq, Eq)]
 pub enum BacktraceStatus {
     /// Capturing a backtrace is not supported, likely because it's not
     /// implemented for the current platform.