Test std::equal with type qualified pointers

[trixirt]

Summary

Problem using std::mismatch with volatile * reduces to same problem with std::equal.

Template expansion does not match from include/algorithms because its addition of 'const' conflicts with 'volatile'

In file included from .../libcxx/test/std/algorithms/alg.nonmodifying/alg.equal/equal_type_qualifie\
r.pass.cpp:9:
.../libcxx/include/algorithm: In instantiation of ‘constexpr bool std::1::equal(_InputIterator1, \
_InputIterator1, _InputIterator2, _BinaryPredicate) [with _InputIterator1 = volatile char*; _InputIterator2 = volatile char*; _BinaryPredicate =\
std::1::equal_to<char, char>]’:
.../libcxx/include/algorithm:1275:24: required from ‘constexpr bool std::1::equal(_InputIterato\
r1, _InputIterator1, _InputIterator2) [with _InputIterator1 = volatile char*; _InputIterator2 = volatile char*]’
.../libcxx/test/std/algorithms/alg.nonmodifying/alg.equal/equal_type_qualifier.pass.cpp:17:3: req\
uired from here
.../libcxx/include/algorithm:1262:20: error: no match for call to ‘(std::1::equal_to<char, char\

) (volatile char&, volatile char&)’

1262 | if (!pred(*first1, *__first2))

|              ~~~~~~^~~~~~~~~~~~~~~~~~~~~~

.../libcxx/include/algorithm:678:10: note: candidate: ‘constexpr bool std::1::equal_to<_T1, _T1\

::operator()(const _T1&, const _T1&) const [with _T1 = char]’ (near match)

678 |     bool operator()(const _T1& __x, const _T1& __y) const {return __x == __y;}                                                           
    |          ^~~~~~~~

.../libcxx/include/algorithm:678:10: note: conversion of argument 2 would be ill-formed:
.../libcxx/include/algorithm:1262:20: error: binding reference of type ‘const char&’ to ‘volatile c\
har’ discards qualifiers
1262 | if (!pred(*first1, *__first2))

libcxx/test/std/algorithms/alg.nonmodifying/alg.equal/equal_type_qualifier.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include <algorithm>
+#include <cassert>
+int main(int, char**) {
+  char* a;
+  assert(std::equal(a, a, a));
+  const char* b;
+  assert(std::equal(b, b, b));
+  volatile char* c;
+  assert(std::equal(c, c, c));
+
+  return 0;
+}