[FEA]: Provide Architecture and OS identification macros

[fbusato]

Is this a duplicate?

• [x] I confirmed there appear to be no duplicate issues for this request and that I agree to the Code of Conduct

Area

libcu++

Is your feature request related to a problem? Please describe.

CCCL provides very useful macros for compiler identification. On the other hand, it misses architecture and OS identification macros that could not be trivial.

Two example:

• Arm processor identification: defined(_M_ARM) || defined(_M_ARM64)
• QNX, Android, L4T/Tegra identification

Describe the solution you'd like

Provide identification macros like https://www.boost.org/doc/libs/release/libs/predef/

Describe alternatives you've considered

No response

Additional context

No response