bug#48056: SWIG is compiled without optimizations

[Ludovic Courtès]

From:

--8<---------------cut here---------------start------------->8---
$ guix describe
Generacio 181   Apr 26 2021 08:47:48    (nuna)
  guix d904abe
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: master
    commit: d904abe0768293b2322dbf355b6e41d94e769d78
$ guix build swig --log-file
https://ci.guix.gnu.org/log/2l8f4sjw0jbfll4ilp7pzwimrh5kjdgf-swig-4.0.1
--8<---------------cut here---------------end--------------->8---

… we can see lots of warnings like this one:

--8<---------------cut here---------------start------------->8---
checking perl5 testcase abstract_inherit_ok
In file included from 
/gnu/store/fa6wj5bxkj5ll1d7292a70knmyl7a0cr-glibc-2.31/include/bits/libc-header-start.h:33:0,
                 from 
/gnu/store/fa6wj5bxkj5ll1d7292a70knmyl7a0cr-glibc-2.31/include/string.h:26,
                 from li_cstring_wrap.cxx:342:
/gnu/store/fa6wj5bxkj5ll1d7292a70knmyl7a0cr-glibc-2.31/include/features.h:397:4:
 warning: #warning _FORTIFY_SOURCE requires compiling with optimization (-O) 
[-Wcpp]
 #  warning _FORTIFY_SOURCE requires compiling with optimization (-O)
    ^~~~~~~
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Compiling without optimizations sounds like a bad idea.  We should add
-O2 somewhere to the CFLAGS.

Ludo’.