Evaluate kotlin/xtensa/llvm support maturity

[xian]

https://github.com/espressif/llvm-xtensa

[xian]

Did some super cursory exploration. Pieces of the toolchain seem to be present and working. Less clear how much work it'd be to link the pieces together. I'm super rusty on makefiles and such, so further investigation would probably best be done in a pair.

I got Espressif's llvm-xtensa stuff built and compiled and assembled a HelloWorld.o from C. Didn't get a native Kotlin Hello World compiled. Didn't get as far as linking and flashing to a device.

I think this is worth some further investigation, though there's still a high likelihood of fail.

[xian]

Opened https://github.com/JetBrains/kotlin-native/issues/3014