ARM Compiler 6 (armclang) support

[tejlmand]

ARM Compiler 6 support has been introduced with https://github.com/zephyrproject-rtos/zephyr/pull/36140.

This means that basic support has now been introduced, however there are still enhancements to be made wrt. the ARM Compiler 6.

This issue is an umbrella issue covering additional ARM Compiler 6 enhancements.

• [x] Documentation landing page for ARM Compiler 6
• [ ] Userspace support (Linker generator in general, but needed by ARM Compiler 6)
• [ ] Enabling microlibc.
• [ ] Support compressed scatter loading. Scatterloading support compression, but the scatter file is set to use no compression to ensure identical behavior with Zephyr startup code. https://github.com/zephyrproject-rtos/zephyr/blob/ebfb23979c8787e78742890e400218952045e8e9/cmake/linker/armlink/scatter_script.cmake#L179
• [ ] Checkup on type system, according to: https://github.com/zephyrproject-rtos/zephyr/issues/37718#issuecomment-907737283
• [ ] Checkup on struct bit field memory layout (see https://github.com/zephyrproject-rtos/zephyr/pull/38679#discussion_r713873327)

[zephyrbot]

Hi @tejlmand,

This issue, marked as an Enhancement, was opened a while ago and did not get any traction. Please confirm the issue is correctly assigned and re-assign it otherwise.

Please take a moment to review if the issue is still relevant to the project. If it is, please provide feedback and direction on how to move forward. If it is not, has already been addressed, is a duplicate, or is no longer relevant, please close it with a short comment explaining the reason.

Thanks!