New port: lang/mecrisp-stellaris: native code Forth for ARM

Mecrisp Stellaris is an implementation of a standalone native code Forth for
ARM. It fits into 16 kb of flash and runs with at least 1 kb of RAM. You can choose to compile to flash or to RAM, and it generates native code with
folding, inlining of short words and it opcodes common instructions. Note that it doesn't need to save any pointers, so it compiles directly into flash memory
without the need for erase cycles. Although it is in spirit of ANS, there are a few differences: Be careful!

PR: 253938
Submitted by: Robert Clausecker <fuz AT fuz DOT su>