bionic: libc: avoid -Wdeprecated-declarations via std::atomic_init

std::atomic_init is deprecated in C++20, and is slated for removal in C++26.
Replace the usage of std::atomic_init with std::atomic_store_explicit with
std::memory_ordering_relaxed.

Link: https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p0883r2.pdf
Link: https://github.com/llvm/llvm-project/commit/56aac567acfd696f54163e33d8df02dc2ad3a72e
Test: mmma bionic
Change-Id: Idf42aea193cfacf8dd7f8528560a396c6064468c
diff --git a/libc/bionic/posix_timers.cpp b/libc/bionic/posix_timers.cpp
index 65749a4..9516059 100644
--- a/libc/bionic/posix_timers.cpp
+++ b/libc/bionic/posix_timers.cpp
@@ -141,7 +141,7 @@
   // Otherwise, this must be SIGEV_THREAD timer...
   timer->callback = evp->sigev_notify_function;
   timer->callback_argument = evp->sigev_value;
-  atomic_init(&timer->deleted, false);
+  atomic_store_explicit(&timer->deleted, false, memory_order_relaxed);
 
   // Check arguments that the kernel doesn't care about but we do.
   if (timer->callback == nullptr) {