Reorganize the 'bit' header to make most of the facilities available for internal use pre-C++20. NFC for external users

llvm-svn: 365854
diff --git a/libcxx/include/algorithm b/libcxx/include/algorithm
index d17666a..0d78626 100644
--- a/libcxx/include/algorithm
+++ b/libcxx/include/algorithm
@@ -3021,7 +3021,7 @@
     typedef __independent_bits_engine<_URNG, _UIntType> _Eng;
     if (_Rp == 0)
         return static_cast<result_type>(_Eng(__g, _Dt)());
-    size_t __w = _Dt - __clz(_Rp) - 1;
+    size_t __w = _Dt - __libcpp_clz(_Rp) - 1;
     if ((_Rp & (std::numeric_limits<_UIntType>::max() >> (_Dt - __w))) != 0)
         ++__w;
     _Eng __e(__g, __w);