Remove barriers to using NDK v8 includes.

Bug: 10315692

Removed CLOCK_BOOTTIME, added some additional guards around cutils includes,
and explicitly included errno.h when we use ETIMEDOUT.

Change-Id: I0a764beea2f8ff7387a9afe985f00b5f03c68725
diff --git a/rsCppUtils.h b/rsCppUtils.h
index ced13c1..c1e72c2 100644
--- a/rsCppUtils.h
+++ b/rsCppUtils.h
@@ -148,7 +148,6 @@
     SYSTEM_TIME_MONOTONIC = 1, // monotonic time since unspecified starting point
     SYSTEM_TIME_PROCESS = 2,   // high-resolution per-process clock
     SYSTEM_TIME_THREAD = 3,    // high-resolution per-thread clock
-    SYSTEM_TIME_BOOTTIME = 4   // same as SYSTEM_TIME_MONOTONIC, but including CPU suspend time
 };
 
 static inline nsecs_t systemTime(int clock)
@@ -158,8 +157,7 @@
             CLOCK_REALTIME,
             CLOCK_MONOTONIC,
             CLOCK_PROCESS_CPUTIME_ID,
-            CLOCK_THREAD_CPUTIME_ID,
-            CLOCK_BOOTTIME
+            CLOCK_THREAD_CPUTIME_ID
     };
     struct timespec t;
     t.tv_sec = t.tv_nsec = 0;