[PATCH v2] README: Update toolchain information

[Jessica Clarke]

On 12 Jul 2021, at 01:30, Bin Meng <bmeng.cn at gmail.com> wrote:
> 
> Recent FW_PIC=y changes actually require toolchains with PIE support
> and it is on by default. Existing doc uses a GNU bare-metal toolchain
> as examples but it does not support PIE.
> 
> Replace references of bare-metal toolchain prefix with Linux toolchain
> prefix everywhere in documentation.
> 
> Also indicate that "riscv64-unknown-freebsd-" as an alternative to
> "riscv64-linux-" GNU toolchain.

Thanks for the changes. The Linux triple is riscv64-linux-gnu (which is
really riscv64-unknown-linux-gnu, but nobody uses that), though. All of
Debian, Fedora and Arch ship their cross toolchains using
riscv64-linux-gnu- as the prefix. The Bootlin toolchains are weird in
providing riscv64-linux-gcc symlinks, though you’ll note those all
symlink to riscv64-buildroot-linux-gnu tools (or indirect through
toolchain-wrapper). I don’t know why they do that, they really should
have a -gnu in there for the triples that don’t have a vendor. I
suggest using riscv64-linux-gnu throughout and adding a note that the
Bootlin toolchains currently omit the -gnu.

Jess