[libcxx] Add deprecation notices to macros deprecated in P0883R2
When P0883R2 was initially implemented in D103769 #pragma clang deprecated didn't exist yet.
We also forgot to cleanup usages in libc++ itself.
This takes care of both.
Differential Revision: https://reviews.llvm.org/D115995
NOKEYCHECK=True
GitOrigin-RevId: 4e730aeb731cb9b7116ed51bbef662d363f72b66
diff --git a/src/ios.cpp b/src/ios.cpp
index a9bd1dc..56fbcca 100644
--- a/src/ios.cpp
+++ b/src/ios.cpp
@@ -137,7 +137,7 @@
// xalloc
#if defined(_LIBCPP_HAS_C_ATOMIC_IMP) && !defined(_LIBCPP_HAS_NO_THREADS)
-atomic<int> ios_base::__xindex_ = ATOMIC_VAR_INIT(0);
+atomic<int> ios_base::__xindex_{0};
#else
int ios_base::__xindex_ = 0;
#endif