configure.ac: Correctly check $host
configure.ac: Correctly check $host

$target is meant for toolchain packages only, not for libraries.

Signed-off-by: Quentin Glidic <241385a0e41ea713327e189bce1062decf7c1eb5@sardemff7.net>

achadwick/libmypaint,achadwick/libmypaint,achadwick/libmypaint,achadwick/libmypaint