Support for `linux/riscv64`
Hi,
I think it will be great if `modernc.org/libc` work in Linux RISC-V (64-bit) environment.
I've done some basic work:
- https://gitlab.com/piggynl/cznic-cc/-/compare/master...linux-riscv64
- https://gitlab.com/piggynl/cznic-libc/-/compare/master...linux-riscv64
In `make linux_riscv64`, `go generate` works fine now, but `go build` produces this:
```
package modernc.org/libc
imports modernc.org/libc/uuid/uuid: build constraints exclude all Go files in /home/piggy/libc/uuid/uuid
```
There are `Code generated by 'ccgo uuid/gen.c ...'` in the beginning of the go files in [the uuid directory](https://gitlab.com/cznic/libc/-/tree/master/uuid), but `gen.c` seems not exist.
Where can I find the `uuid/gen.c`? And what else can I do? Thank you for your work!
Also, if you are interested, I can help you setup a QEMU environment and/or provide you ssh access to a SiFive Unmatched RISC-V development board (the one that [ci.rvperf.org](https://ci.rvperf.org) uses).
issue