[libc++] Add a missing <_Compare> template argument.

Sometimes `_Compare` is an lvalue reference type, so letting it be
deduced is pretty much always wrong. (Well, less efficient than
it could be, anyway.)

Differential Revision: https://reviews.llvm.org/D93562

Author: Quuxplusone

libcxx/include/algorithm

@@ -4483,7 +4483,7 @@ __buffered_inplace_merge(_BidirectionalIterator __first, _BidirectionalIterator
         value_type* __p = __buff;
         for (_BidirectionalIterator __i = __first; __i != __middle; __d.template __incr<value_type>(), (void) ++__i, (void) ++__p)
             ::new ((void*)__p) value_type(_VSTD::move(*__i));
-        _VSTD::__half_inplace_merge(__buff, __p, __middle, __last, __first, __comp);
+        _VSTD::__half_inplace_merge<_Compare>(__buff, __p, __middle, __last, __first, __comp);
     }
     else
     {
@@ -4492,9 +4492,10 @@ __buffered_inplace_merge(_BidirectionalIterator __first, _BidirectionalIterator
             ::new ((void*)__p) value_type(_VSTD::move(*__i));
         typedef reverse_iterator<_BidirectionalIterator> _RBi;
         typedef reverse_iterator<value_type*> _Rv;
-        _VSTD::__half_inplace_merge(_Rv(__p), _Rv(__buff),
+        typedef __invert<_Compare> _Inverted;
+        _VSTD::__half_inplace_merge<_Inverted>(_Rv(__p), _Rv(__buff),
                                     _RBi(__middle), _RBi(__first),
-                                    _RBi(__last), _VSTD::__invert<_Compare>(__comp));
+                                    _RBi(__last), _Inverted(__comp));
     }
 }