tools, build: Propagate build failures from tools/build/Makefile.build

[ Upstream commit a278f3d8191228212c553a5d4303fa603214b717 ]

The '&&' command seems to have a bad effect when $(cmd_$(1)) exits with
non-zero effect: the command failure is masked (despite `set -e`) and all but
the first command of $(dep-cmd) is executed (successfully, as they are mostly
printfs), thus overall returning 0 in the end.

This means in practice that despite compilation errors, tools's build Makefile
will return success. We see this very reliably with libbpf's Makefile, which
doesn't get compilation error propagated properly. This in turns causes issues
with selftests build, as well as bpftool and other projects that rely on
building libbpf.

The fix is simple: don't use &&. Given `set -e`, we don't need to chain
commands with &&. The shell will exit on first failure, giving desired
behavior and propagating error properly.

Fixes: 275e2d9559 ("tools build: Move dependency copy into function")
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Link: https://lore.kernel.org/bpf/20200731024244.872574-1-andriin@fb.com
Signed-off-by: Sasha Levin <sashal@kernel.org>

tools/build/Build.include

@@ -74,7 +74,8 @@ dep-cmd = $(if $(wildcard $(fixdep)),
 #                   dependencies in the cmd file
 if_changed_dep = $(if $(strip $(any-prereq) $(arg-check)),         \
                   @set -e;                                         \
-                  $(echo-cmd) $(cmd_$(1)) && $(dep-cmd))
+                  $(echo-cmd) $(cmd_$(1));                         \
+                  $(dep-cmd))
 
 # if_changed      - execute command if any prerequisite is newer than
 #                   target, or command line has changed