[libc++] Remove _LIBCPP_CONSTINIT (#171802) `_LIBCPP_CONSTINIT` is only ever used inside `src/`, so we can just replace it with `constinit` instead. NOKEYCHECK=True GitOrigin-RevId: 67cf9b8f827e816ada6dbbee3a4f0cdb7c1d0595

diff --git a/src/cxa_guard_impl.h b/src/cxa_guard_impl.h
index 191a589..5f51e81 100644
--- a/src/cxa_guard_impl.h
+++ b/src/cxa_guard_impl.h

@@ -637,7 +637,7 @@
   static T instance;
 };
 template <class T>
-_LIBCPP_CONSTINIT T GlobalStatic<T>::instance = {};
+constinit T GlobalStatic<T>::instance = {};
 
 enum class Implementation { NoThreads, GlobalMutex, Futex };
 

diff --git a/src/fallback_malloc.cpp b/src/fallback_malloc.cpp
index 6a261e6..81195c9 100644
--- a/src/fallback_malloc.cpp
+++ b/src/fallback_malloc.cpp

@@ -35,9 +35,9 @@
 
 // When POSIX threads are not available, make the mutex operations a nop
 #ifndef _LIBCXXABI_HAS_NO_THREADS
-static _LIBCPP_CONSTINIT std::__libcpp_mutex_t heap_mutex = _LIBCPP_MUTEX_INITIALIZER;
+static constinit std::__libcpp_mutex_t heap_mutex = _LIBCPP_MUTEX_INITIALIZER;
 #else
-static _LIBCPP_CONSTINIT void* heap_mutex = 0;
+static constinit void* heap_mutex = 0;
 #endif
 
 class mutexor {

diff --git a/test/guard_test_basic.pass.cpp b/test/guard_test_basic.pass.cpp
index dca906a..feb9e1c 100644
--- a/test/guard_test_basic.pass.cpp
+++ b/test/guard_test_basic.pass.cpp

@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 //
-// UNSUPPORTED: c++03
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
 
 // Necessary because we include a private header of libc++abi, which
 // only understands _LIBCXXABI_HAS_NO_THREADS.

diff --git a/test/guard_threaded_test.pass.cpp b/test/guard_threaded_test.pass.cpp
index 78dafba..d898e60 100644
--- a/test/guard_threaded_test.pass.cpp
+++ b/test/guard_threaded_test.pass.cpp

@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// UNSUPPORTED: c++03
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
 // UNSUPPORTED: no-threads
 // UNSUPPORTED: no-exceptions
 

diff --git a/test/test_fallback_malloc.pass.cpp b/test/test_fallback_malloc.pass.cpp
index c8a6a07..379fe57 100644
--- a/test/test_fallback_malloc.pass.cpp
+++ b/test/test_fallback_malloc.pass.cpp

@@ -13,7 +13,7 @@
 
 #include <__thread/support.h>
 
-// UNSUPPORTED: c++03
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
 // UNSUPPORTED: modules-build && no-threads
 
 // Necessary because we include a private source file of libc++abi, which