tracing: Fix unused tracepoints when module uses only exported ones

tracing: Fix unused tracepoints when module uses only exported ones

Building the KVM intel module failed to build with UT=1:

no __tracepoint_strings in file: arch/x86/kvm/kvm-intel.o
make[3]: *** [/work/git/test-linux.git/scripts/Makefile.modfinal:62: arch/x86/kvm/kvm-intel.ko] Error 1

The reason is that the module only uses the tracepoints defined and
exported by the main kvm module. The tracepoint-update.c code fails the
build if a tracepoint is used, but there's no tracepoints defined. But
this is acceptable in modules if the tracepoints are defined in the vmlinux
proper or another module and exported.

Do not fail to build if a tracepoint is used but no tracepoints are
defined if the code is a module. This should still never happen for the
vmlinux itself.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Link: https://patch.msgid.link/20251209204023.76941824@fedora
Fixes: e30f8e61e2518 ("tracing: Add a tracepoint verification check at build time")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>