libstdc++: Add atomic_fetch_xor to <stdatomic.h>

This function (and the explicit memory over version) are present in both
C++ <atomic> and C <stdatomic.h>, so should be in C++ <stdatomic.h> too.
There is a library issue incoming for this, but the resolution is
obvious.

libstdc++-v3/ChangeLog:

	* include/c_compatibility/stdatomic.h (atomic_fetch_xor): Add
	using-declaration.
	(atomic_fetch_xor_explicit): Likewise.
	* testsuite/29_atomics/headers/stdatomic.h/c_compat.cc: Check
	arithmetic and logical operations for atomic_int.

1 files changed, 2 insertions, 0 deletions

diff --git a/libstdc++-v3/include/c_compatibility/stdatomic.h b/libstdc++-v3/include/c_compatibility/stdatomic.h
index 95c72615b4e..c97cbac984e 100644
--- a/libstdc++-v3/include/c_compatibility/stdatomic.h
+++ b/libstdc++-v3/include/c_compatibility/stdatomic.h
@@ -111,6 +111,8 @@ using std::atomic_fetch_sub;
 using std::atomic_fetch_sub_explicit;
 using std::atomic_fetch_or;
 using std::atomic_fetch_or_explicit;
+using std::atomic_fetch_xor;
+using std::atomic_fetch_xor_explicit;
 using std::atomic_fetch_and;
 using std::atomic_fetch_and_explicit;
 using std::atomic_flag_test_and_set;