Rename identifiers named `__output`

Summary:
In the CHERI clang compiler __output and __input are keywords and therefore
we can't compile libc++ with our compiler.

Reviewers: mclow.lists, EricWF, theraven

Reviewed By: EricWF

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D39537

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@318144 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/algorithm b/include/algorithm
index f5776b4..8f6938d 100644
--- a/include/algorithm
+++ b/include/algorithm
@@ -3210,28 +3210,28 @@
           class _UniformRandomNumberGenerator>
 _LIBCPP_INLINE_VISIBILITY
 _SampleIterator __sample(_PopulationIterator __first,
-                         _PopulationIterator __last, _SampleIterator __output,
+                         _PopulationIterator __last, _SampleIterator __output_iter,
                          _Distance __n,
                          _UniformRandomNumberGenerator & __g,
                          input_iterator_tag) {
 
   _Distance __k = 0;
   for (; __first != __last && __k < __n; ++__first, (void)++__k)
-    __output[__k] = *__first;
+    __output_iter[__k] = *__first;
   _Distance __sz = __k;
   for (; __first != __last; ++__first, (void)++__k) {
     _Distance __r = _VSTD::uniform_int_distribution<_Distance>(0, __k)(__g);
     if (__r < __sz)
-      __output[__r] = *__first;
+      __output_iter[__r] = *__first;
   }
-  return __output + _VSTD::min(__n, __k);
+  return __output_iter + _VSTD::min(__n, __k);
 }
 
 template <class _PopulationIterator, class _SampleIterator, class _Distance,
           class _UniformRandomNumberGenerator>
 _LIBCPP_INLINE_VISIBILITY
 _SampleIterator __sample(_PopulationIterator __first,
-                         _PopulationIterator __last, _SampleIterator __output,
+                         _PopulationIterator __last, _SampleIterator __output_iter,
                          _Distance __n,
                          _UniformRandomNumberGenerator& __g,
                          forward_iterator_tag) {
@@ -3240,18 +3240,18 @@
     _Distance __r =
         _VSTD::uniform_int_distribution<_Distance>(0, --__unsampled_sz)(__g);
     if (__r < __n) {
-      *__output++ = *__first;
+      *__output_iter++ = *__first;
       --__n;
     }
   }
-  return __output;
+  return __output_iter;
 }
 
 template <class _PopulationIterator, class _SampleIterator, class _Distance,
           class _UniformRandomNumberGenerator>
 _LIBCPP_INLINE_VISIBILITY
 _SampleIterator __sample(_PopulationIterator __first,
-                         _PopulationIterator __last, _SampleIterator __output,
+                         _PopulationIterator __last, _SampleIterator __output_iter,
                          _Distance __n, _UniformRandomNumberGenerator& __g) {
   typedef typename iterator_traits<_PopulationIterator>::iterator_category
         _PopCategory;
@@ -3263,7 +3263,7 @@
   typedef typename common_type<_Distance, _Difference>::type _CommonType;
   _LIBCPP_ASSERT(__n >= 0, "N must be a positive number.");
   return _VSTD::__sample(
-      __first, __last, __output, _CommonType(__n),
+      __first, __last, __output_iter, _CommonType(__n),
       __g, _PopCategory());
 }
 
@@ -3272,9 +3272,9 @@
           class _UniformRandomNumberGenerator>
 inline _LIBCPP_INLINE_VISIBILITY
 _SampleIterator sample(_PopulationIterator __first,
-                       _PopulationIterator __last, _SampleIterator __output,
+                       _PopulationIterator __last, _SampleIterator __output_iter,
                        _Distance __n, _UniformRandomNumberGenerator&& __g) {
-    return _VSTD::__sample(__first, __last, __output, __n, __g);
+    return _VSTD::__sample(__first, __last, __output_iter, __n, __g);
 }
 #endif // _LIBCPP_STD_VER > 14