bitwise: convert popcount template into explicit overloads

popcount, popcountl, and popcountll need to be used for each appropriate
fundamental type. It's easiest to just provide overloads for popcount
for the few cases we have available than to deal with templates.

bitwise.hpp

@@ -67,19 +67,29 @@ namespace cruft {
 
 
     ///////////////////////////////////////////////////////////////////////////
-    template <
+    constexpr unsigned
-        typename T,
+    popcount (unsigned t)
-        typename = std::enable_if_t<
-            std::is_integral_v<T>
-        >
-    >
-    constexpr T
-    popcount (T t)
     {
         return __builtin_popcount (t);
     }
 
 
+    //-------------------------------------------------------------------------
+    constexpr unsigned long
+    popcount (unsigned long t)
+    {
+        return __builtin_popcountl (t);
+    }
+
+
+    //-------------------------------------------------------------------------
+    constexpr unsigned long long
+    popcount (unsigned long long t)
+    {
+        return __builtin_popcountll (t);
+    }
+
+
     ///////////////////////////////////////////////////////////////////////////
     /// returns the integral value composed of the bits from `val' in the
     /// inclusive range [lo, hi].