libsysprof-capture: Replace G_{UN,}LIKELY with SYSPROF_{UN,}LIKELY

This does the same thing for modern compilers, but without the GLib
dependency.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Helps: #40

src/libsysprof-capture/sysprof-clock.h

@@ -80,7 +80,7 @@ sysprof_clock_get_current_time (void)
   struct timespec ts;
   SysprofClock clock = sysprof_clock;
 
-  if G_UNLIKELY (clock == -1)
+  if SYSPROF_UNLIKELY (clock == -1)
     clock = CLOCK_MONOTONIC;
   clock_gettime (clock, &ts);