Replace CLOCK_MONOTONIC with SYSTEM_TIME_MONOTONIC

Using SYSTEM_TIME_MONOTONIC works for Android (where it translates to
CLOCK_MONOTONIC) and host targets, while CLOCK_MONOTONIC is not defined
on macOS.

Bug: 117921091
Test: existing tests should pass
Change-Id: I1fad472881830fb0701a320cf37319e083932ad4
diff --git a/libs/hwui/thread/WorkQueue.h b/libs/hwui/thread/WorkQueue.h
index 42f8503..46b8bc0 100644
--- a/libs/hwui/thread/WorkQueue.h
+++ b/libs/hwui/thread/WorkQueue.h
@@ -31,7 +31,7 @@
 namespace android::uirenderer {
 
 struct MonotonicClock {
-    static nsecs_t now() { return systemTime(CLOCK_MONOTONIC); }
+    static nsecs_t now() { return systemTime(SYSTEM_TIME_MONOTONIC); }
 };
 
 class WorkQueue {