Add a config default for QNX 7.0

[samkearney]

I am adding std support for QNX 7.0, a previous release of QNX Neutrino RTOS, and using ctest2 to test necessary changes to libc.

See for reference:

• https://github.com/rust-lang/rust/blob/master/src/doc/rustc/src/platform-support/nto-qnx.md
• https://github.com/JohnTitor/ctest2/pull/46

[samkearney]

I don't think the CI failures are related to my change, I think it's because of a new warning on nightly. See https://github.com/rust-lang/rust/pull/109732