lavu/checkasm: add (private) kperf timing for macOS

Signed-off-by: J. Dekker <jdek@itanimul.li>

tests/checkasm/checkasm.c

@@ -638,9 +638,17 @@ static int bench_init_linux(void)
     }
     return 0;
 }
-#endif
+#elif CONFIG_MACOS_KPERF
+static int bench_init_kperf(void)
+{
+    if (ff_kperf_init()) {
+        fprintf(stderr, "checkasm must be run as root to use kperf on macOS\n");
+        return -1;
+    }
 
-#if !CONFIG_LINUX_PERF
+    return 0;
+}
+#else
 static int bench_init_ffmpeg(void)
 {
 #ifdef AV_READ_TIME
@@ -657,6 +665,8 @@ static int bench_init(void)
 {
 #if CONFIG_LINUX_PERF
     int ret = bench_init_linux();
+#elif CONFIG_MACOS_KPERF
+    int ret = bench_init_kperf();
 #else
     int ret = bench_init_ffmpeg();
 #endif