Set icon for QEMU binary on Mac OS

Before switching the build system over to Meson, an icon was
added to the QEMU binary on Mac OS. This patch adds back that
feature; it piggybacks on the existing scripts/entitlement.sh,
which already does in-place changes to the executable on Darwin.

Signed-off-by: John Arbuckle <programmingkidx@gmail.com>
Message-Id: <20210705195328.36442-1-programmingkidx@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>