Backtrace capture on SGX broken after (including) nightly-2023-11-20

It looks like that after #117895 (that seems to be the only SGX backtrace-related change between the two versions) enabling backtraces and attempting to capture one on the x86_64-fortanix-unknown-sgx target (sometimes) results in the enclave hanging.

Code

Unfortunately I don't currently have a minimal reproducer example, but roughly:

std::env::set_var("RUST_BACKTRACE", "1");
// ... unspecified logic, multiple nested frames ...
std::backtrace::Backtrace::capture();

I expected to see this happen: backtrace is captured without issues.

Instead, this happened: the Backtrace::capture() method appears to hang.

Version it worked on

It most recently worked on: nightly-2023-11-19

Version with regression

nightly-2023-11-20

Start by comparing nightly-2023-11-19 and nightly-2023-11-20 for the x86_64-fortanix-unknown-sgx target, focusing on the SGX backtrace-related change in #117895. Reproduce with RUST_BACKTRACE=1 and std::backtrace::Backtrace::capture() in a nested call context; done means capture no longer hangs and the regression is covered by a focused test or reproducer.