tracing: Add warnings for unused tracepoints for modules

If a modules has TRACE_EVENT() but does not use it, add a warning about it
at build time.

Currently, the build must be made by adding "UT=1" to the make command
line in order for this to trigger.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nicolas Schier <nicolas.schier@linux.dev>
Cc: Nick Desaulniers <nick.desaulniers+lkml@gmail.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Link: https://lore.kernel.org/20251022004453.422000794@kernel.org
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Author: rostedt

scripts/Makefile.modfinal

@@ -28,6 +28,10 @@ ccflags-remove-y := $(CC_FLAGS_CFI)
 .module-common.o: $(srctree)/scripts/module-common.c FORCE
 	$(call if_changed_rule,cc_o_c)
 
+ifneq ($(WARN_ON_UNUSED_TRACEPOINTS),)
+cmd_check_tracepoint = $(objtree)/scripts/tracepoint-update --module $<;
+endif
+
 quiet_cmd_ld_ko_o = LD [M]  $@
       cmd_ld_ko_o =							\
 	$(LD) -r $(KBUILD_LDFLAGS)					\
@@ -57,6 +61,7 @@ if_changed_except = $(if $(call newer_prereqs_except,$(2))$(cmd-check),      \
 ifdef CONFIG_DEBUG_INFO_BTF_MODULES
 	+$(if $(newer-prereqs),$(call cmd,btf_ko))
 endif
+	+$(call cmd,check_tracepoint)
 
 targets += $(modules:%.o=%.ko) $(modules:%.o=%.mod.o) .module-common.o