Add QNX NTO platform support

[nyurik]

This is part of the https://github.com/rust-lang/rust/pull/127897 work. This fix resolves the following failing unit tests:

[ui] tests/ui/backtrace/backtrace.rs
[ui] tests/ui/backtrace/dylib-dep.rs
[ui] tests/ui/backtrace/line-tables-only.rs
[ui] tests/ui/backtrace/std-backtrace.rs
[ui] tests/ui/panics/issue-47429-short-backtraces.rs#legacy
[ui] tests/ui/panics/issue-47429-short-backtraces.rs#v0
[ui] tests/ui/panics/runtime-switch.rs#legacy
[ui] tests/ui/panics/runtime-switch.rs#v0
[ui] tests/ui/panics/short-ice-remove-middle-frames-2.rs
[ui] tests/ui/panics/short-ice-remove-middle-frames.rs
[ui] tests/ui/runtime/backtrace-debuginfo.rs

[nyurik]

@workingjubilee thx for all the feedback, libc 0.2.156 just released with the consistent backtrace on QNX. I updated this PR to use it.

[nyurik]

@workingjubilee thx, fixed merge conflict, should be ok now