graphics/exiv2: fix build on ARM and PPC platforms
exiv2 added -fcf-protection, which is not supported on either ARM or PPC.
https://github.com/Exiv2/exiv2/commit/1ea63ccb345a4498b41cb8842622ba7ecc9fd484 fixes that but only for ARM.
Merge this commit and add modify it to also fix PPC. This is likely the wrong approach, since -fcf-protection seems to be available only on amd64, but this is the approach that upstream chose.
MFH: 2020Q3 (fix build blanket)