libbpf: Use the standard fixdep build rule

libbpf: Use the standard fixdep build rule

libbpf's all target depends on the fixdep target defined in
tools/scripts/Makefile.include.  However the $(BPF_IN_SHARED) and
$(BPF_IN_STATIC) targets don't use it, but instead rebuild fixdep in
the staticobjs or sharedobjs subdirectory using a different command.

Change the $(BPF_IN_SHARED) and $(BPF_IN_STATIC) targets to depend on
fixdep and to symlink the executable into the respective output
subdirectory.

Signed-off-by: Ben Hutchings <benh@debian.org>
Gbp-Pq: Topic bugfix/all
Gbp-Pq: Name libbpf-use-the-standard-fixdep-build-rule.patch