[libc++] Make __libcpp_verbose_abort() noexcept like std::terminate() (llvm#109151)

Make __libcpp_verbose_abort() noexcept (it is already noreturn), to
match std::terminate(). Clang's function effect analysis can use this to
ignore such functions as being beyond its scope. (See
llvm#99656).

Author: dougsonos

libcxx/docs/ReleaseNotes/20.rst

@@ -82,6 +82,9 @@ Deprecations and Removals
   were private but could cause ambiguity in name lookup. Code that expects such ambiguity will possibly not compile in
   LLVM 20.
 
+- The function ``__libcpp_verbose_abort()`` is now ``noexcept``, to match ``std::terminate()``. (The combination of
+  ``noexcept`` and ``[[noreturn]]`` has special significance for function effects analysis.)
+
 Upcoming Deprecations and Removals
 ----------------------------------
 

libcxx/include/__verbose_abort

@@ -21,7 +21,7 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 // This function should never be called directly from the code -- it should only be called through
 // the _LIBCPP_VERBOSE_ABORT macro.
 [[__noreturn__]] _LIBCPP_AVAILABILITY_VERBOSE_ABORT _LIBCPP_OVERRIDABLE_FUNC_VIS
-_LIBCPP_ATTRIBUTE_FORMAT(__printf__, 1, 2) void __libcpp_verbose_abort(const char* __format, ...);
+_LIBCPP_ATTRIBUTE_FORMAT(__printf__, 1, 2) void __libcpp_verbose_abort(const char* __format, ...) _NOEXCEPT;
 
 // _LIBCPP_VERBOSE_ABORT(format, args...)
 //

libcxx/src/verbose_abort.cpp

@@ -28,7 +28,7 @@ extern "C" void android_set_abort_message(const char* msg);
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-_LIBCPP_WEAK void __libcpp_verbose_abort(char const* format, ...) {
+_LIBCPP_WEAK void __libcpp_verbose_abort(char const* format, ...) noexcept {
   // Write message to stderr. We do this before formatting into a
   // buffer so that we still get some information out if that fails.
   {

libcxx/test/libcxx/assertions/customize_verbose_abort.link-time.pass.cpp

@@ -15,9 +15,7 @@
 #include <__verbose_abort>
 #include <cstdlib>
 
-void std::__libcpp_verbose_abort(char const*, ...) {
-  std::exit(EXIT_SUCCESS);
-}
+void std::__libcpp_verbose_abort(char const*, ...) _NOEXCEPT { std::exit(EXIT_SUCCESS); }
 
 int main(int, char**) {
   std::__libcpp_verbose_abort("%s", "message");

libcxx/test/support/check_assertion.h

@@ -334,7 +334,7 @@ class DeathTest {
 };
 
 #ifdef _LIBCPP_VERSION
-void std::__libcpp_verbose_abort(char const* format, ...) {
+void std::__libcpp_verbose_abort(char const* format, ...) noexcept {
   va_list args;
   va_start(args, format);