[portable-rustls] add CI build testing for multiple targets with no atomic ptr (src update deferred) - CI FAILURE EXPECTED

[brody4hire]

STATUS:

• EXPECTED to FAIL at this point - should fail due to missing Arc for target with no atomic ptr - need to check recent updates

DEFERRED ITEMS - deferred to another PR:

• TODO: use portable_atomic_util::Arc to resolve this issue
• TODO: update documentation

OPEN QUESTION(S):

• feature-based configuration to select "std" Arc (alloc::sync::Arc) vs portable-atomic (portable-atomic-util) Arc - may be able to defer this
• add some kind of "critical-section" feature to enable "critical-section" in once_cell & possible transitive portable-atomic dep(s) - may be able to defer this
• always use once_cell sync feature instead of once_cell::race if "critical-section" feature is enabled - this looks like a pretty small but nice optimization

[brody4hire]

It took me a little while to figure out that using "portable-atomic" feature with a dash (-) didn't work due to mvdnes/spin-rs#170 - proposed mvdnes/spin-rs#172 to fix this.

[brody4hire]

I am pretty unhappy with the number of crates still directly or indirectly using outdated [email protected], hope to see this situation improve in the near future.