imagemagick: convert to autotargets and bump to 6.6.4

program-transform-name='s,,,' is needed, otherwise configure defines it
as $(platform)-$(cpu)-. During install, all executables are prepended
with this variable.

[Peter: disable libtool patch, remove unneeded/wrong staging install cmd]
Signed-off-by: Martin Banky <Martin.Banky@gmail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>