iconv doesn't provide .pc file which breaks detection of libarchive

[kjmeagher]

libarchive provides a .pc file to help detection, but it depends on iconv which does not provide a pc file. This causes breakage so that you can use pkg-config to find libarchive

pkg-config libarchive --cflags
Package iconv was not found in the pkg-config search path.
Perhaps you should add the directory containing `iconv.pc'
to the PKG_CONFIG_PATH environment variable
Package 'iconv', required by 'libarchive', not found