Auto merge of #148020 - bjorn3:oom_backtrace, r=Mark-Simulacrum

Show backtrace on allocation failures when possible

And if an allocation while printing the backtrace fails, don't try to print another backtrace as that will never succeed.

Split out of rust-lang/rust#147725 to allow landing this independently of a decision whether or not to remove `-Zoom=panic`.

Author: bors

tests/fail/alloc/alloc_error_handler.stderr

@@ -1,11 +1,15 @@
 memory allocation of 4 bytes failed
+note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 error: abnormal termination: the program aborted execution
   --> RUSTLIB/std/src/alloc.rs:LL:CC
    |
-LL |     crate::process::abort()
-   |     ^^^^^^^^^^^^^^^^^^^^^^^ abnormal termination occurred here
+LL |         crate::process::abort()
+   |         ^^^^^^^^^^^^^^^^^^^^^^^ abnormal termination occurred here
    |
    = note: BACKTRACE:
+   = note: inside closure at RUSTLIB/std/src/alloc.rs:LL:CC
+   = note: inside `std::sys::backtrace::__rust_end_short_backtrace::<{closure@std::alloc::rust_oom::{closure#0}}, !>` at RUSTLIB/std/src/sys/backtrace.rs:LL:CC
    = note: inside `std::alloc::rust_oom` at RUSTLIB/std/src/alloc.rs:LL:CC
    = note: inside `std::alloc::_::__rust_alloc_error_handler` at RUSTLIB/std/src/alloc.rs:LL:CC
    = note: inside `std::alloc::handle_alloc_error::rt_error` at RUSTLIB/alloc/src/alloc.rs:LL:CC