perf build: Warn if libtracefs is not found

Signed-off-by: Guilherme Amadio <amadio@gentoo.org>
Tested-by: Thorsten Leemhuis <linux@leemhuis.info>
Tested-by: Leo Yan <leo.yan@arm.com>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Cc: linux-trace-devel@vger.kernel.org
Link: https://lore.kernel.org/r/20240717174739.186988-2-amadio@gentoo.orgSigned-off-by: Namhyung Kim <namhyung@kernel.org>

tools/perf/Makefile.config

@@ -1206,6 +1206,8 @@ ifneq ($(NO_LIBTRACEEVENT),1)
     LIBTRACEFS_VERSION_3 := $(word 3, $(subst ., ,$(LIBTRACEFS_VERSION)))
     LIBTRACEFS_VERSION_CPP := $(shell expr $(LIBTRACEFS_VERSION_1) \* 255 \* 255 + $(LIBTRACEFS_VERSION_2) \* 255 + $(LIBTRACEFS_VERSION_3))
     CFLAGS += -DLIBTRACEFS_VERSION=$(LIBTRACEFS_VERSION_CPP)
+  else
+    $(warning libtracefs is missing. Please install libtracefs-dev/libtracefs-devel)
   endif
 endif