[Accidentally pushed patch v1, this commit contains the rest of the
changes. Revised commit message follows.]
Apart from debug information, one can also strip some symbols. This can
be a significant difference, the closure of gcc-toolchain@7 got reduced
by 15 MB in my tests.
As per [1], --strip-debug is included in --strip-unneeded, and
the debug files created also contain a copy of the information removed
by --strip-unneeded.
Linux From Scratch suggests that this option shouldn't be used on static
libraries [2], however other sources [3] indicate otherwise. Building a
toolchain with this patch succeeds, and the result works fine for
'gcc -static hello-world.c'.
[1]: https://stackoverflow.com/a/52555093
[2]: http://www.linuxfromscratch.org/lfs/view/9.1/chapter05/stripping.html
[3]: https://www.technovelty.org/linux/stripping-shared-libraries.html
* guix/build/gnu-build-system.scm (strip): Use --strip-unneeded.
* guix/build-system/gnu.scm (static-package, gnu-build, gnu-cross-build): Likewise.
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