[gcc r12-2494] libstdc++: Reduce headers included by <future>

[Jonathan Wakely <redi@gcc.gnu.org>]

https://gcc.gnu.org/g:3ea62a2b2ed739209936e0ed27539965ae4c9840

commit r12-2494-g3ea62a2b2ed739209936e0ed27539965ae4c9840
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Jul 23 12:32:05 2021 +0100

    libstdc++: Reduce headers included by <future>
    
    The <future> header only needs std::atomic_flag, so can include
    <bits/atomic_base.h> instead of the whole of <atomic>.
    
    libstdc++-v3/ChangeLog:
    
            * include/std/future: Include <bits/atomic_base.h> instead of
            <atomic>.

Diff:
---
 libstdc++-v3/include/std/future | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/std/future b/libstdc++-v3/include/std/future
index 09e54c3703b..ace0c311f1a 100644
--- a/libstdc++-v3/include/std/future
+++ b/libstdc++-v3/include/std/future
@@ -38,9 +38,10 @@
 #include <mutex>	      // call_once
 #include <condition_variable> // __at_thread_exit_elt
 #include <system_error>
-#include <atomic>
+#include <bits/atomic_base.h> // atomic_flag
 #include <bits/allocated_ptr.h>
 #include <bits/atomic_futex.h>
+#include <bits/exception_defines.h>
 #include <bits/invoke.h>
 #include <bits/unique_ptr.h>
 #include <bits/shared_ptr.h>