libbpf: Re-build libbpf.so when libbpf.map changes

libbpf: Re-build libbpf.so when libbpf.map changes

[ Upstream commit 61c7aa5020e98ac2fdcf07d07eec1baf2e9f0a08 ]

Ensure libbpf.so is re-built whenever libbpf.map is modified.  Without this,
changes to libbpf.map are not detected and versioned symbols mismatch error
will be reported until `make clean && make` is used, which is a suboptimal
developer experience.

Fixes: 306b267cb3c4 ("libbpf: Verify versioned symbols")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20210815070609.987780-8-andrii@kernel.org
Signed-off-by: Sasha Levin <sashal@kernel.org>