version-1.4.0 branch updated

[Maxim Cournoyer]

Hello,

I've pushed a version-1.4.0 branch refresh that tackled a few issues:

- #52269 (sitecustomize.py: Honor .pth files.)
- #52574 (glib: Fix cross-compilation.)
- #52411 (gnu: pciutils: Fix the conditional for the kmod input.)
- #52519 (gnu: glibmm-2.64: Fix libsigc++ propagation.)

Since touching sitecustomize.py was a world rebuilding change, I've
squeezed a few items picked from our guix-patches tracker or newly
authored, such as:

- update meson to 0.60.3 and undo workarounds introduced for
  0.60.2.
- update python to 3.9.9
- update cmake to 3.21.4
- update mesa to 21.3.2
- absorb binutils-next into binutils

and more!

You can find the changes introduced in the branch by issuing git log
'origin/master..origin/version-1.4.0'.

If nobody has another world rebuilding change deemed necessary in time
for the release, I suggest we enable substitutes on the branch soon, and
then get busy trying to get 'make dist' to succeed so that we can issue
a first RC.

We'll also need to write the website materials such as the release blog
post and edit that NEWS file with the most noteworthy changes that have
gone into this release since 1.3.0.

Thank you!

Maxim