Rollup merge of rust-lang#133464 - RalfJung:whitespace-panic, r=joboet

std::thread: avoid leading whitespace in some panic messages

This:
```
        panic!(
            "use of std::thread::current() is not possible after the thread's
         local data has been destroyed"
        )
```
will print a newline followed by a bunch of spaces, since the entire string literal is interpreted literally.

I think the intention was to print the message without the newline and the spaces, so let's add some `\` to make that happen.

r? `@joboet`

Author: jhpratt

library/std/src/thread/current.rs

@@ -243,17 +243,17 @@ fn init_current(current: *mut ()) -> Thread {
         // a particular API should be entirely allocation-free, feel free to open
         // an issue on the Rust repository, we'll see what we can do.
         rtabort!(
-            "\n
-            Attempted to access thread-local data while allocating said data.\n
-            Do not access functions that allocate in the global allocator!\n
-            This is a bug in the global allocator.\n
-        "
+            "\n\
+            Attempted to access thread-local data while allocating said data.\n\
+            Do not access functions that allocate in the global allocator!\n\
+            This is a bug in the global allocator.\n\
+            "
         )
     } else {
         debug_assert_eq!(current, DESTROYED);
         panic!(
-            "use of std::thread::current() is not possible after the thread's
-         local data has been destroyed"
+            "use of std::thread::current() is not possible after the thread's \
+            local data has been destroyed"
         )
     }
 }