ESP32 toolchain

[Frédéric Fauberteau <triaxx%netbsd.org@localhost>]

Hi folks,

I am working on NodeMCU ESP32 development board. I wanted to test minimal assembly bare metal program for this platform and I though it was a good opportunity to use the cross toolchain available in pkgsrc (cross/xtensa-esp-elf-{binutils, gcc}).

But when I tried to convert the ELF executable to binary image with esptool, I got the following error:

```
A fatal error occurred: Image does not appear to be an Xtensa or an RISCV ELF image. (e_machine = 0x5e00)
```

Actually, the produced binary is a ELF 32-bit MSB executable. But it seems that ESP32 chips are little endian and the cross GCC should produce a LSB executable.

Therefore I have packaged in wip another cross toolchain: wip/xtensa-esp32-elf-{binutils, gcc} that uses the Espressif overlays. It is based on cross/xtensa-esp-elf-{binutils, gcc}: thank you tnn@ for your initial packaging.

If anyone is interested in this platform and can test the wip packages, I would be very interested in their feedback before importing them into pkgsrc.