tools/build: Add bpftool-skeletons feature test

Add bpftool-skeletons feature test, testing the presence of a bpftool
capable of generating skeletons.

This is to be used for tools that do not require building their own
bootstrap bpftool from the kernel source tree.

Cc: John Kacur <[e-mail]>
Cc: Luis Goncalves <[e-mail]>
Cc: Gabriele Monaco <[e-mail]>
Cc: Clark Williams <[e-mail]>
Link: https://lore.kernel.org/[e-mail]
Signed-off-by: Tomas Glozar <[e-mail]>
Signed-off-by: Steven Rostedt (Google) <[e-mail]>

tools/build/Makefile.feature

···
          libbpf-bpf_create_map		\
          libpfm4                        \
          libdebuginfod			\
-         clang-bpf-co-re
+         clang-bpf-co-re		\
+         bpftool-skeletons
 
 
 FEATURE_TESTS ?= $(FEATURE_TESTS_BASIC)

tools/build/feature/Makefile

···
 $(OUTPUT)test-libpfm4.bin:
 	$(BUILD) -lpfm
 
+$(OUTPUT)test-bpftool-skeletons.bin:
+	$(BPFTOOL) version | grep '^features:.*skeletons' \
+		> $(@:.bin=.make.output) 2>&1
 ###############################
 
 clean:

tools/scripts/Makefile.include

···
 LLVM_OBJCOPY	?= llvm-objcopy
 LLVM_STRIP	?= llvm-strip
 
+# Some tools require bpftool
+BPFTOOL		?= bpftool
+
 ifeq ($(CC_NO_CLANG), 1)
 EXTRA_WARNINGS += -Wstrict-aliasing=3