Fix building on NetBSD

The static inline function popcount64() conflicts with a function
with NetBSD's libc.

https://man.netbsd.org/popcount.3

libpopcnt.h

@@ -149,7 +149,7 @@ extern "C" {
  * It uses 12 arithmetic operations, one of which is a multiply.
  * http://en.wikipedia.org/wiki/Hamming_weight#Efficient_implementation
  */
-static inline uint64_t popcount64(uint64_t x)
+static inline uint64_t libpopcount64(uint64_t x)
 {
   uint64_t m1 = 0x5555555555555555ll;
   uint64_t m2 = 0x3333333333333333ll;
@@ -222,7 +222,7 @@ static inline uint64_t popcnt64(uint64_t x)
 
 static inline uint64_t popcnt64(uint64_t x)
 {
-  return popcount64(x);
+  return libpopcount64(x);
 }
 
 #endif
@@ -645,14 +645,14 @@ static inline uint64_t popcnt(const void* data, uint64_t size)
    * We use unaligned memory accesses here to improve performance.
    */
   for (; i < size - size % 8; i += 8)
-    cnt += popcount64(*(const uint64_t*)(ptr + i));
+    cnt += libpopcount64(*(const uint64_t*)(ptr + i));
 
   if (i < size)
   {
     uint64_t val = 0;
     size_t bytes = (size_t)(size - i);
     memcpy(&val, &ptr[i], bytes);
-    cnt += popcount64(val);
+    cnt += libpopcount64(val);
   }
 
   return cnt;
@@ -750,7 +750,7 @@ static inline uint64_t popcnt(const void* data, uint64_t size)
     uint64_t val = 0;
     size_t bytes = (size_t)(size - i);
     memcpy(&val, &ptr[i], bytes);
-    cnt += popcount64(val);
+    cnt += libpopcount64(val);
   }
 
   return cnt;