[Bug target/117421] [RISCV] Use byte comparison instead of word comparison

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117421

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note riscv is sometimes does not support unaligned accesses which might be part
of the issue here.

Reduced to just:
```
int ext_is_gzip(char * ext) {
    return __builtin_memcmp(ext, "gzip", 4) == 0;
}
```

I should note that -mno-strict-align still does not do it but that is because
it might be slow still to do unaligned access.

using -mtune=thead-c906 "works".

I am suspect this is expected behavior.