Modify the setting of LD_LIBRARY_PATH to append pre-existing values at the
time the rule is evaluated rather than when the Makefile is created.
This is required when building packages with dpkg-buildpackage and fakeroot,
since fakeroot (which now sets LD_LIBRARY_PATH) is not used for the "build"
rule where the Makefile is created, but is for the clean/binary* targets.
Gbp-Pq: Topic debian
Gbp-Pq: Name fakeroot.diff