Define missing static constexpr variables

This will prevent link errors when undefined symbols when compiling at
-O0.  Normally, this isn't a problem, but causes failure when compiling
at -O0 to maximize debugability

Change-Id: Iafe187b6b9344fead1bbc73004e376fad821756b
Signed-off-by: Mark Mendell <mark.p.mendell@intel.com>
diff --git a/runtime/base/timing_logger.cc b/runtime/base/timing_logger.cc
index c8dee6d..076bc11 100644
--- a/runtime/base/timing_logger.cc
+++ b/runtime/base/timing_logger.cc
@@ -31,6 +31,8 @@
 
 namespace art {
 
+constexpr size_t CumulativeLogger::kLowMemoryBucketCount;
+constexpr size_t CumulativeLogger::kDefaultBucketCount;
 CumulativeLogger::CumulativeLogger(const std::string& name)
     : name_(name),
       lock_name_("CumulativeLoggerLock" + name),