Add AUR link: https://aur.archlinux.org/packages/riscv-gnu-toolchain

Add AUR link: [https://aur.archlinux.org/packages/riscv-gnu-toolchain/](https://aur.archlinux.org/packages/riscv-gnu-toolchain/)

Added:

Also available for Arch users on the AUR: [https://aur.archlinux.org/packages/riscv-gnu-toolchain/](https://aur.archlinux.org/packages/riscv-gnu-toolchain/)

Fix typo in build-libc dependencies

The variable MULTLIB_NAMES does not exist but is used when
generating the dependencies for the target build-libc for glibc.
Even when adding the missing 'I' (for MULTILIB_NAMES) there is
still no variable with this name.

So the whole dependency generation is useless, becauese it was not
needed so far. Looking into detail why it is so, we can find the
answer in the dependency list of the target 'stamps/build-gcc-linux-stage2'.

Let's fix this by setting the dependencies for build-libc right.
The dependencies for 'stamps/build-gcc-linux-stage2' stay as they are
not wrong.

Fixes: 3456b66f

 ("Add a "make report" phony target")
Signed-off-by: Christoph Muellner <cmuellner@linux.com>

Fix submodule URLs

Bump binutils to 2.37 release.

Add flock to OS X dependencies

Bump gcc to 11.1

- PR 94853 and PR 86153 are reoslved
- gfortran.dg/elemental_subroutine_3.f90 seems pass now.
- g++.dg/tls/thread_local4* added to allow list since they might random
  fail on qemu, and hard to reproduce.

Bump binutils to get rv32e fixes.

gitignore build directories

Bump Binutils to 2.36.1

Signed-off-by: Christoph Muellner <cmuellner@linux.com>

Bump gcc for testsuite fixes.

Bump qemu to 5.2.0

Bump glibc and linux kernel

 - RV32 require 5.10 which is too new for most linux distro.

This resolves #799