[libcxx] Use __libcpp_verbose_abort for error messages

Rather than using the following sequence of calls:

```
fprintf(stderr, "...");
::abort();
```

We should use the following:

```
__libcpp_verbose_abort("...")
```

This simplifies the code and ensures the behavior is consistent across
all call sites. Since `__libcpp_verbose_abort` is defined as weak, it
also allows users to provide their implementation if they want to change
the behavior which may be helpful in environments like embedded where
error reporting usually requires special handling.

libcxx/src/support/runtime/exception_fallback.ipp

@@ -7,7 +7,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include <cstdio>
+#include <__verbose_abort>
 
 namespace std {
 
@@ -39,13 +39,11 @@ terminate_handler get_terminate() noexcept { return __libcpp_atomic_load(&__term
 #endif // _LIBCPP_HAS_NO_EXCEPTIONS
     (*get_terminate())();
     // handler should not return
-    fprintf(stderr, "terminate_handler unexpectedly returned\n");
-    ::abort();
+    __libcpp_verbose_abort("terminate_handler unexpectedly returned\n");
 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
   } catch (...) {
     // handler should not throw exception
-    fprintf(stderr, "terminate_handler unexpectedly threw an exception\n");
-    ::abort();
+    __libcpp_verbose_abort("terminate_handler unexpectedly threw an exception\n");
   }
 #endif // _LIBCPP_HAS_NO_EXCEPTIONS
 }
@@ -54,8 +52,7 @@ bool uncaught_exception() noexcept { return uncaught_exceptions() > 0; }
 
 int uncaught_exceptions() noexcept {
 #warning uncaught_exception not yet implemented
-  fprintf(stderr, "uncaught_exceptions not yet implemented\n");
-  ::abort();
+  __libcpp_verbose_abort("uncaught_exceptions not yet implemented\n");
 }
 
 exception::~exception() noexcept {}

libcxx/src/support/runtime/exception_msvc.ipp

@@ -11,8 +11,7 @@
 #  error this header can only be used when targeting the MSVC ABI
 #endif
 
-#include <stdio.h>
-#include <stdlib.h>
+#include <__verbose_abort>
 
 extern "C" {
 typedef void(__cdecl* terminate_handler)();
@@ -48,13 +47,11 @@ terminate_handler get_terminate() noexcept { return ::_get_terminate(); }
 #endif // _LIBCPP_HAS_NO_EXCEPTIONS
     (*get_terminate())();
     // handler should not return
-    fprintf(stderr, "terminate_handler unexpectedly returned\n");
-    ::abort();
+    __libcpp_verbose_abort("terminate_handler unexpectedly returned\n");
 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
   } catch (...) {
     // handler should not throw exception
-    fprintf(stderr, "terminate_handler unexpectedly threw an exception\n");
-    ::abort();
+    __libcpp_verbose_abort("terminate_handler unexpectedly threw an exception\n");
   }
 #endif // _LIBCPP_HAS_NO_EXCEPTIONS
 }

libcxx/src/support/runtime/exception_pointer_unimplemented.ipp

@@ -7,33 +7,28 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include <stdio.h>
-#include <stdlib.h>
+#include <__verbose_abort>
 
 namespace std {
 
 exception_ptr::~exception_ptr() noexcept {
 #warning exception_ptr not yet implemented
-  fprintf(stderr, "exception_ptr not yet implemented\n");
-  ::abort();
+  __libcpp_verbose_abort("exception_ptr not yet implemented\n");
 }
 
 exception_ptr::exception_ptr(const exception_ptr& other) noexcept : __ptr_(other.__ptr_) {
 #warning exception_ptr not yet implemented
-  fprintf(stderr, "exception_ptr not yet implemented\n");
-  ::abort();
+  __libcpp_verbose_abort("exception_ptr not yet implemented\n");
 }
 
 exception_ptr& exception_ptr::operator=(const exception_ptr& other) noexcept {
 #warning exception_ptr not yet implemented
-  fprintf(stderr, "exception_ptr not yet implemented\n");
-  ::abort();
+  __libcpp_verbose_abort("exception_ptr not yet implemented\n");
 }
 
 exception_ptr exception_ptr::__from_native_exception_pointer(void *__e) noexcept {
 #warning exception_ptr not yet implemented
-  fprintf(stderr, "exception_ptr not yet implemented\n");
-  ::abort();
+  __libcpp_verbose_abort("exception_ptr not yet implemented\n");
 }
 
 nested_exception::nested_exception() noexcept : __ptr_(current_exception()) {}
@@ -46,8 +41,7 @@ nested_exception::~nested_exception() noexcept {}
 
 [[noreturn]] void nested_exception::rethrow_nested() const {
 #warning exception_ptr not yet implemented
-  fprintf(stderr, "exception_ptr not yet implemented\n");
-  ::abort();
+  __libcpp_verbose_abort("exception_ptr not yet implemented\n");
 #if 0
   if (__ptr_ == nullptr)
       terminate();
@@ -57,14 +51,12 @@ nested_exception::~nested_exception() noexcept {}
 
 exception_ptr current_exception() noexcept {
 #warning exception_ptr not yet implemented
-  fprintf(stderr, "exception_ptr not yet implemented\n");
-  ::abort();
+  __libcpp_verbose_abort("exception_ptr not yet implemented\n");
 }
 
 [[noreturn]] void rethrow_exception(exception_ptr p) {
 #warning exception_ptr not yet implemented
-  fprintf(stderr, "exception_ptr not yet implemented\n");
-  ::abort();
+  __libcpp_verbose_abort("exception_ptr not yet implemented\n");
 }
 
 } // namespace std