[gcc r12-2604] fix breakage from "libstdc++: Remove unnecessary uses of <utility>"

[Hans-Peter Nilsson <hp@gcc.gnu.org>]

https://gcc.gnu.org/g:4186cb9cc017a0d4b3f45ef6b2f959ef10f17fc5

commit r12-2604-g4186cb9cc017a0d4b3f45ef6b2f959ef10f17fc5
Author: Hans-Peter Nilsson <hp@bitrange.com>
Date:   Thu Jul 29 18:02:47 2021 +0200

    fix breakage from "libstdc++: Remove unnecessary uses of <utility>"
    
    Commit r12-2534 was incomplete and (by inspection derived
    from an MMIX build) failing for targets without an insn for
    compare_and_swap for pointer-size objects, IOW for targets
    for which "ATOMIC_POINTER_LOCK_FREE != 2" is true:
    
    x/gcc/libstdc++-v3/src/c++17/memory_resource.cc: In member function
     'std::pmr::memory_resource*
    std::pmr::{anonymous}::atomic_mem_res::exchange(std::pmr::memory_resource*)':
    x/gcc/libstdc++-v3/src/c++17/memory_resource.cc:140:21: error:
     'exchange' is not a member of 'std'
      140 |         return std::exchange(val, r);
          |                     ^~~~~~~~
    make[5]: *** [Makefile:577: memory_resource.lo] Error 1
    make[5]: Leaving directory
     '/home/hp/tmp/newmmix-r12-2579-p3/gccobj/mmix/libstdc++-v3/src/c++17'
    
    This fix was derived from edits elsewhere in that patch.
    
    Tested mmix-knuth-mmixware, restoring build (together with
    target-reviving patches as MMIX is currently and at that commit
    broken for target-specific reasons).
    
    libstdc++-v3/:
            * src/c++17/memory_resource.cc: Use __exchange instead
            of std::exchange.

Diff:
---
 libstdc++-v3/src/c++17/memory_resource.cc | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/libstdc++-v3/src/c++17/memory_resource.cc b/libstdc++-v3/src/c++17/memory_resource.cc
index 5dfc29fc0ec..1ba79903f87 100644
--- a/libstdc++-v3/src/c++17/memory_resource.cc
+++ b/libstdc++-v3/src/c++17/memory_resource.cc
@@ -29,7 +29,7 @@
 #include <new>
 #if ATOMIC_POINTER_LOCK_FREE != 2
 # include <bits/std_mutex.h>	// std::mutex, std::lock_guard
-# include <bits/move.h>		// std::exchange
+# include <bits/move.h>		// std::__exchange
 #endif
 
 namespace std _GLIBCXX_VISIBILITY(default)
@@ -117,7 +117,7 @@ namespace pmr
       memory_resource* exchange(memory_resource* r)
       {
 	lock_guard<mutex> lock(mx);
-	return std::exchange(val, r);
+	return std::__exchange(val, r);
       }
     };
 #else
@@ -137,7 +137,7 @@ namespace pmr
 
       memory_resource* exchange(memory_resource* r)
       {
-	return std::exchange(val, r);
+	return std::__exchange(val, r);
       }
     };
 #endif // ATOMIC_POINTER_LOCK_FREE == 2