Squashed commit of the following:

commit 54d1983cd8d8551c28109a506a752a971897f4ed
Author: David Monniaux <david.monniaux@univ-grenoble-alpes.fr>
Date:   Sat Jun 12 00:48:02 2021 +0200

    sudo make install

commit 49af5c63eff29a49f3cb466a6b6af44570d85352
Author: David Monniaux <david.monniaux@univ-grenoble-alpes.fr>
Date:   Sat Jun 12 00:43:17 2021 +0200

    pixman

commit d78ab98e5751dd3ae0299a3e8c271472ebd8bb63
Author: David Monniaux <david.monniaux@univ-grenoble-alpes.fr>
Date:   Sat Jun 12 00:36:30 2021 +0200

    libglib

commit 0808bf51be42b04c2db4ccc914633407c1309585
Author: David Monniaux <david.monniaux@univ-grenoble-alpes.fr>
Date:   Sat Jun 12 00:31:46 2021 +0200

    don't show verbose untar

commit 972c244c72d9a30fee41dc7cbcc3698a49b6cde6
Author: David Monniaux <david.monniaux@univ-grenoble-alpes.fr>
Date:   Sat Jun 12 00:30:32 2021 +0200

    ninja-build

commit a1c261d01abc1c62ea94d56cfc9cce90887db680
Author: David Monniaux <david.monniaux@univ-grenoble-alpes.fr>
Date:   Sat Jun 12 00:28:14 2021 +0200

    install ninja

commit 92990598283f624d598853851c3edb2650f45b4b
Author: David Monniaux <david.monniaux@univ-grenoble-alpes.fr>
Date:   Sat Jun 12 00:25:17 2021 +0200

    untar

commit a225a0dcea26dd8888be535aa1aec4a58007679d
Author: David Monniaux <david.monniaux@univ-grenoble-alpes.fr>
Date:   Sat Jun 12 00:20:32 2021 +0200

    install wget first

commit 3b2c30ab6a953bde9d09034d38c5919a9425163d
Author: David Monniaux <david.monniaux@univ-grenoble-alpes.fr>
Date:   Sat Jun 12 00:17:09 2021 +0200

    install recent qemu

fix for comments on x86-64 MacOS

As reported in #399, it seems better to use `##` instead of `#` as
comment delimiter under macOS.

For the time being we keep using `#` for Linux and Cygwin.

Closes: #399

Merge branch 'kvx-work' of https://gricad-gitlab.univ-grenoble-alpes.fr/sixcy/CompCert into kvx-work

Before, the line number had to start with a nonzero digit.  However,
the GCC 11 preprocessor was observed to produce `# 0 ...` directives.

Fixes: #398