This follows up commit d5b5a15a40 which doesn't
work because %current-system etc expands before the actual build.
Fixes <https://bugs.gnu.org/31719>.
* guix/build-system/meson.scm (meson-build)[builder]: Compare against the
already existing "system" variable rather than (%current-system).
* guix/build-system/meson.scm (lower): Remove DEFAULT-PATCHELF from inputs
on armhf.
(meson-build): Ignore the 'fix-runpath' phase when building for arm systems.