ART: Clean up arm64 kNumberOfXRegisters usage.

Avoid undefined behavior for arm64 stemming from 1u << 32 in
loops with upper bound kNumberOfXRegisters.

Create iterators for enumerating bits in an integer either
from high to low or from low to high and use them for
<arch>Context::FillCalleeSaves() on all architectures.

Refactor runtime/utils.{h,cc} by moving all bit-fiddling
functions to runtime/base/bit_utils.{h,cc} (together with
the new bit iterators) and all time-related functions to
runtime/base/time_utils.{h,cc}. Improve test coverage and
fix some corner cases for the bit-fiddling functions.

Bug: 13925192
Change-Id: I704884dab15b41ecf7a1c47d397ab1c3fc7ee0f7
diff --git a/runtime/thread_linux.cc b/runtime/thread_linux.cc
index 0526f49..0731f30 100644
--- a/runtime/thread_linux.cc
+++ b/runtime/thread_linux.cc
@@ -14,10 +14,11 @@
  * limitations under the License.
  */
 
-#include "thread.h"
-
 #include <signal.h>
 
+#include "thread.h"
+#include "utils.h"
+
 namespace art {
 
 void Thread::SetNativePriority(int) {