RISC-V backport to 4.6.4 - Questions about libgcc

[Ekaitz Zarraga]

Hi all,

I'm backporting RISC-V support to GCC 4.6.4 in order to obtain a bootstrappable GCC for RISC-V and I'm finding some issues I can't solve myself. Maybe you can help.

I managed to backport the core of gcc, so now I can compile to assembly.

The problems came with the backport of `libgcc` because I don't understand the building process very well (and it also changed from gcc 4.6.4 to 7.5). I managed to make it build by copying many parts of the build system from `libgcc/config/riscv` to `gcc/config/riscv` because I was obtaining errors like: "Extra parts are not coherent". At the moment I managed it to compile but when I try to build software with it it's unable to find some of the functions that should be available in libgcc:

```
printf_fphex.c:212: undefined reference to `__unordtf2'
printf_fphex.c:212: undefined reference to `__letf2'
```

Can anyone point me to what I might be missing here? I'm out of ideas.

If anyone is interested on taking a deeper look, the repository with my changes can be found here:
https://github.com/ekaitz-zarraga/gcc

Thank you very much,
Ekaitz