tools/resolve_btfids: Build libbpf and libsubcmd in separate directories

tools/resolve_btfids: Build libbpf and libsubcmd in separate directories

[ Upstream commit fc6b48f692f89cc48bfb7fd1aa65454dfe9b2d77 ]

Setting up separate build directories for libbpf and libpsubcmd,
so it's separated from other objects and we don't get them mixed
in the future.

It also simplifies cleaning, which is now simple rm -rf.

Also there's no need for FEATURE-DUMP.libbpf and bpf_helper_defs.h
files in .gitignore anymore.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210205124020.683286-2-jolsa@kernel.org
Signed-off-by: Sasha Levin <sashal@kernel.org>