bug#63948: qtbase@6 retains reference to ‘gcc-final’

[Ludovic Courtès]

The closure of ‘qtbase’ is unreasonable large, and this is in part
because it retains a reference to GCC:

--8<---------------cut here---------------start------------->8---
$ guix graph -t references --path qtbase 
/gnu/store/gqld7hz5vm4g904g7nc77z7wzvdrrwyb-zlib-1.2.13
/gnu/store/0zqk6bmgvwxh1kx963hhknwnqh3h0iik-qtbase-6.3.2
/gnu/store/5lqhcv91ijy82p92ac6g5xw48l0lwwz4-gcc-11.3.0
/gnu/store/gqld7hz5vm4g904g7nc77z7wzvdrrwyb-zlib-1.2.13
$ guix build  -e '(@@ (gnu packages commencement) gcc-final)'
/gnu/store/930nwsiysdvy2x5zv1sf6v7ym75z8ayk-gcc-11.3.0-lib
/gnu/store/5lqhcv91ijy82p92ac6g5xw48l0lwwz4-gcc-11.3.0
$ guix size qtbase | tail -1
total: 1204.7 MiB
$ guix describe
Generation 265  Jun 04 2023 23:48:31    (current)
  guix eed55a6
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: master
    commit: eed55a6544d5bda2245ec853e5fa4b28e1865bea
--8<---------------cut here---------------end--------------->8---

This comes from a CMake file:

--8<---------------cut here---------------start------------->8---
$ grep -r 5lqhcv91ijy82p92ac6g5xw48l0lwwz4 
/gnu/store/0zqk6bmgvwxh1kx963hhknwnqh3h0iik-qtbase-6.3.2
/gnu/store/0zqk6bmgvwxh1kx963hhknwnqh3h0iik-qtbase-6.3.2/lib/cmake/Qt6/qt.toolchain.cmake:
    set(__qt_initial_c_compiler 
"/gnu/store/5lqhcv91ijy82p92ac6g5xw48l0lwwz4-gcc-11.3.0/bin/gcc")
/gnu/store/0zqk6bmgvwxh1kx963hhknwnqh3h0iik-qtbase-6.3.2/lib/cmake/Qt6/qt.toolchain.cmake:
    set(__qt_initial_cxx_compiler 
"/gnu/store/5lqhcv91ijy82p92ac6g5xw48l0lwwz4-gcc-11.3.0/bin/c++")
--8<---------------cut here---------------end--------------->8---

We should remove this reference.

Ludo’.