std: Don't assume thread::current() works on panic

Inspecting the current thread's info may not always work due to the TLS value
having been destroyed (or is actively being destroyed). The code for printing
a panic message assumed, however, that it could acquire the thread's name
through this method.

Instead this commit propagates the `Option` outwards to allow the
`std::panicking` module to handle the case where the current thread isn't
present.

While it solves the immediate issue of #24313, there is still another underlying
issue of panicking destructors in thread locals will abort the process.

Closes #24313

src/libstd/sys/unix/stack_overflow.rs

@@ -81,7 +81,7 @@ mod imp {
         // We're calling into functions with stack checks
         stack::record_sp_limit(0);
 
-        let guard = thread_info::stack_guard();
+        let guard = thread_info::stack_guard().unwrap_or(0);
         let addr = (*info).si_addr as usize;
 
         if guard == 0 || addr < guard - PAGE_SIZE || addr >= guard {