Implemented BitCount as an intrinsic. With unit test.

Rationale:
Recognizing this important operation as an intrinsic has
various advantages:
(1) having the no-side-effects/no-throw allows for
    much more GVN/LICM/BCE.
(2) Some architectures, like x86_64, provide direct
    support for this operation.

Performance improvements on X86_64:
CheckersEvalBench (32-bit bitboard): 27,210KNS -> 36,798KNS  =  + 35%
ReversiEvalBench  (64-bit bitboard): 52,562KNS -> 89,086KNS  =  + 69%

Change-Id: I65d549b0469b7909b12c6611cdc34a8640a5751f
diff --git a/compiler/dex/quick/dex_file_method_inliner.h b/compiler/dex/quick/dex_file_method_inliner.h
index ac70577..2803623 100644
--- a/compiler/dex/quick/dex_file_method_inliner.h
+++ b/compiler/dex/quick/dex_file_method_inliner.h
@@ -224,6 +224,7 @@
       kNameCachePutObjectVolatile,
       kNameCachePutOrderedObject,
       kNameCacheArrayCopy,
+      kNameCacheBitCount,
       kNameCacheNumberOfLeadingZeros,
       kNameCacheNumberOfTrailingZeros,
       kNameCacheRotateRight,