The included iconv should not be used on Linux or OS X, but (depending on
local configuration) it might be needed for crosscompiling a mingw target
from Linux. Now the user can choose whether to use the included iconv or not.
cmake does already support that.
eilseq.m4 was taken from the original libiconv 1.14 package.
This causes build problems with automake < 1.14 because two files have the same name. This only works well when using subdir-objects, which we only do after 1.14.
We do not want to build libiconv on target which support autotools anyway, but rely on a built-in one.
This fixes building on oldish ubuntu 12.04.
The new 3rdparty libraries are not added to the autotools build system, so
that they appear in the source package. They cannot be compiled yet with
autotools (although this would make sense for cross compilation with mingw),
but adding configure support for enabling/disabling these like we do for
boost is a bit more work, so I did not do it for now. Nevertheless, the
three new Makefile.am are already prepared for compilation.
