Merge a few A64 utils into the CompilerIntrinsics.

src/a64/utils-a64.h

Index: src/a64/utils-a64.h
diff --git a/src/a64/utils-a64.h b/src/a64/utils-a64.h
index 16c51a9c8b52770b44d09fe738adc1cc34dbd80c..b25f29e468c06207559810469dd78364ddd55e86 100644
--- a/src/a64/utils-a64.h
+++ b/src/a64/utils-a64.h
@@ -71,11 +71,10 @@ static inline double rawbits_to_double(uint64_t bits) {
 
 
 // Bits counting.
-int CountLeadingZeros(uint64_t value, int width);
-int CountLeadingSignBits(int64_t value, int width);
-int CountTrailingZeros(uint64_t value, int width);
-int CountSetBits(uint64_t value, int width);
-int MaskToBit(uint64_t mask);
+inline int MaskToBit(uint64_t mask) {
+  ASSERT(CountSetBits(mask, 64) == 1);
+  return CountTrailingZeros(mask, 64);
+}
 
 
 // NaN tests.