debian/control.in/libc, debian/rules.d/debhelper.mk: Make libcX-dev declare a Breaks against libcX-dev-${DEB_HOST_ARCH}-cross (<< ${CURRENT_UPSTREAM_VERSION}~). Closes: #954393.
debian/control.in/libc, debian/control.in/main: drop Conflicts, Breaks and Replaces against package version older than the one available in oldstable.