This is needed after libltdl took over ltdl.h, and without it we get:
Unpacking libltdl (2.4.7-2) over (2.4.7-1) ...
dpkg: error processing archive /data/data/com.termux/cache/apt/archives/libltdl_2.4.7-2_aarch64.deb (--unpack):
trying to overwrite '/data/data/com.termux/files/usr/include/ltdl.h', which is also in package libtool 2.4.7-1
Fixes: termux/termux-packages#20230
The libltdl has been split out from libtool to allow packages to depend
only on libltdl and not the whole libtool. But for this to work we need
TERMUX_SUBPKG_DEPEND_ON_PARENT=no
Otherwise there is a dependency cycle between libtool and libltdl, so
they are always installed together