Describe relationship between RTEMS and gcc cross-compiler

[Gedare Bloom]

Occasionally new users are confused why they can't use their distributions cross-compiler for their target, e.g., the riscv64-linux-gnu or the arm-none-eabi-gcc. This task is to write a paragraph or two in the User's Guide to explain why this doesn't work.

You will need to identify a good place in the guide to put this information, and work with the community to understand the restrictions. Probably somewhere near the start of the user's guide or in the quick start will be good.

At a high-level, the reasons that one must use the rtemsX-gcc are:

• newlib will be configured correctly for rtems, which is where much of our POSIX and libc support comes from.
• threading in GCC support libraries is tailored to RTEMS
• to provide the preprocessor define __rtems__

There may be some other small reasons that could come up from discussion.

[Chris Johns]

Plus specific multilib variants to match BSPs