ftrace: Only compile ftrace selftest if selftests are enabled

No need to compile in the ftrace selftest helper file if selftests are
not being executed.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/Makefile

@@ -5,10 +5,12 @@ ifdef CONFIG_FUNCTION_TRACER
 ORIG_CFLAGS := $(KBUILD_CFLAGS)
 KBUILD_CFLAGS = $(subst -pg,,$(ORIG_CFLAGS))
 
+ifdef CONFIG_FTRACE_SELFTEST
 # selftest needs instrumentation
 CFLAGS_trace_selftest_dynamic.o = -pg
 obj-y += trace_selftest_dynamic.o
 endif
+endif
 
 # If unlikely tracing is enabled, do not trace these files
 ifdef CONFIG_TRACING_BRANCHES