Wrong endianness on ESP32-C3

[wxorx]

I've got some of those cute super mini boards with ESP32-C3 (RISC-V) and decided to push it hard as a simple web radio. While MP3 decoding worked fine, AAC produced loud noise only.

I dig a bit and found the reason is in libhelix-aac/assembly.h. The U64 typedef checks for __XTENSA__ macro, not available on C3 and falls to big endian assuming its a powerpc. I've modified it locally like this below to make it work:
#if defined(__XTENSA__) || defined(__riscv)

Maybe using big endian only if __powerpc__ or __POWERPC__ is defined?

[pschatzmann]

Can you submit a pull request ?

[wxorx]

I did, please review, thank you!