tools, bpftool: Correctly evaluate $(BUILD_BPF_SKELS) in Makefile

Currently, if the clang-bpf-co-re feature is not available, the build
fails with e.g.

  CC       prog.o
prog.c:1462:10: fatal error: profiler.skel.h: No such file or directory
 1462 | #include "profiler.skel.h"
      |          ^~~~~~~~~~~~~~~~~

This is due to the fact that the BPFTOOL_WITHOUT_SKELETONS macro is not
defined, despite BUILD_BPF_SKELS not being set. Fix this by correctly
evaluating $(BUILD_BPF_SKELS) when deciding on whether to add
-DBPFTOOL_WITHOUT_SKELETONS to CFLAGS.

Fixes: 05aca6da3b5a ("tools/bpftool: Generalize BPF skeleton support and generate vmlinux.h")
Signed-off-by: Tobias Klauser <[email protected]>
Signed-off-by: Daniel Borkmann <[email protected]>
Reviewed-by: Quentin Monnet <[email protected]>
Acked-by: Andrii Nakryiko <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]

0 files changed, 0 insertions, 0 deletions