fixup! [clang] Implement __builtin_popcountg

Author: overmighty

clang/docs/LanguageExtensions.rst

@@ -3473,6 +3473,37 @@ builtin, the mangler emits their usual pattern without any special treatment.
   // Computes a unique stable name for the given type.
   constexpr const char * __builtin_sycl_unique_stable_name( type-id );
 
+``__builtin_popcountg``
+-----------------------
+
+``__builtin_popcountg`` returns the number of 1 bits in the argument. The
+argument can be of any integer type.
+
+**Syntax**:
+
+.. code-block:: c++
+
+  int __builtin_popcountg(type x)
+
+**Examples**:
+
+.. code-block:: c++
+
+  int x = 1;
+  int x_pop = __builtin_popcountg(x);
+
+  unsigned long y = 3;
+  int y_pop = __builtin_popcountg(y);
+
+  _BitInt(128) z = 7;
+  int z_pop = __builtin_popcountg(z);
+
+**Description**:
+
+``__builtin_popcountg`` is meant to be a type-generic alternative to the
+``__builtin_popcount{,l,ll}`` builtins, with support for other integer types,
+such as ``__int128`` and C23 ``_BitInt(N)``.
+
 Multiprecision Arithmetic Builtins
 ----------------------------------