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/private/bionic_lock.h b/libc/private/bionic_lock.h
index 8ed4939..d0c6d5e 100644
--- a/libc/private/bionic_lock.h
+++ b/libc/private/bionic_lock.h
@@ -46,7 +46,7 @@
 
  public:
   void init(bool process_shared) {
-    atomic_init(&state, Unlocked);
+    atomic_store_explicit(&state, Unlocked, memory_order_relaxed);
     this->process_shared = process_shared;
   }