Add -Z proc-macro-backtrace to allow showing proc-macro panics

Fixes #75050

Previously, we would unconditionally suppress the panic hook during
proc-macro execution. This commit adds a new flag
-Z proc-macro-backtrace, which allows running the panic hook for
easier debugging.

compiler/rustc_interface/src/passes.rs

@@ -291,6 +291,7 @@ fn configure_and_expand_inner<'a>(
             trace_mac: sess.opts.debugging_opts.trace_macros,
             should_test: sess.opts.test,
             span_debug: sess.opts.debugging_opts.span_debug,
+            proc_macro_backtrace: sess.opts.debugging_opts.proc_macro_backtrace,
             ..rustc_expand::expand::ExpansionConfig::default(crate_name.to_string())
         };
 

compiler/rustc_interface/src/tests.rs

@@ -502,6 +502,7 @@ fn test_debugging_options_tracking_hash() {
     untracked!(print_llvm_passes, true);
     untracked!(print_mono_items, Some(String::from("abc")));
     untracked!(print_type_sizes, true);
+    untracked!(proc_macro_backtrace, true);
     untracked!(query_dep_graph, true);
     untracked!(query_stats, true);
     untracked!(save_analysis, true);