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/build/Android.gtest.mk b/build/Android.gtest.mk
index bfc8956..ccea540 100644
--- a/build/Android.gtest.mk
+++ b/build/Android.gtest.mk
@@ -124,6 +124,7 @@
   runtime/arch/x86_64/instruction_set_features_x86_64_test.cc \
   runtime/barrier_test.cc \
   runtime/base/bit_field_test.cc \
+  runtime/base/bit_utils_test.cc \
   runtime/base/bit_vector_test.cc \
   runtime/base/hash_set_test.cc \
   runtime/base/hex_dump_test.cc \
@@ -131,6 +132,7 @@
   runtime/base/mutex_test.cc \
   runtime/base/scoped_flock_test.cc \
   runtime/base/stringprintf_test.cc \
+  runtime/base/time_utils_test.cc \
   runtime/base/timing_logger_test.cc \
   runtime/base/variant_map_test.cc \
   runtime/base/unix_file/fd_file_test.cc \