profiler: Make profiler-is-running a macro

profiler: Make profiler-is-running a macro

When we use if (GDK_PROFILER_IS_RUNNING) this means we get an
inlined if (FALSE) when the compiler support is not compiled in, which
gets rid of all the related code completely.

We also expand to  G_UNLIKELY(gdk_profiler_is_running ()) in the supported
case which might cause somewhat better code generation.