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/jit/jit.h b/runtime/jit/jit.h
index c698cfc..8f92453 100644
--- a/runtime/jit/jit.h
+++ b/runtime/jit/jit.h
@@ -33,6 +33,10 @@
 class CompilerCallbacks;
 struct RuntimeArgumentMap;
 
+namespace mirror {
+class ArtMethod;
+}  // namespace mirror
+
 namespace jit {
 
 class JitCodeCache;