Don't use HAVE_POSIX_CLOCKS.

I'm not sure whether it's a bug that this array doesn't contain all the POSIX
clocks. There's also a (different) copy of this function in system/core. But
today I'm just trying to kill HAVE_POSIX_CLOCKS.

Change-Id: Iff6a10b1e7a9d5e9c76b796c5aa75b7d7b6546b5
diff --git a/rsCppUtils.h b/rsCppUtils.h
index 7f1d58c..8b49056 100644
--- a/rsCppUtils.h
+++ b/rsCppUtils.h
@@ -63,7 +63,7 @@
 
 static inline nsecs_t systemTime(int clock)
 {
-#if defined(HAVE_POSIX_CLOCKS)
+#if defined(__linux__)
     static const clockid_t clocks[] = {
             CLOCK_REALTIME,
             CLOCK_MONOTONIC,