[libcxx] Fix build with GLIBC

[philnik]

Which glibc version affects this? Also, why not just use __builtin_abort instead? That would remove the need for the forward declaration all together.

[vitalybuka]

__builtin_abort

[vitalybuka]

In D140946#4024896, @philnik wrote:

Which glibc version affects this?

2.27, but it's 23 years the same https://github.com/bminor/glibc/blame/master/stdlib/stdlib.h#L611

Also, why not just use __builtin_abort instead? That would remove the need for the forward declaration all together.

Thanks for the hint, done

[philnik]

In D140946#4024932, @vitalybuka wrote:

In D140946#4024896, @philnik wrote:

Which glibc version affects this?

2.27, but it's 23 years the same https://github.com/bminor/glibc/blame/master/stdlib/stdlib.h#L611

Did the compiler warn or something, or how did you find this?

LGTM with CI passing.

[vitalybuka]

In D140946#4024937, @philnik wrote:

In D140946#4024932, @vitalybuka wrote:

In D140946#4024896, @philnik wrote:

Which glibc version affects this?

2.27, but it's 23 years the same https://github.com/bminor/glibc/blame/master/stdlib/stdlib.h#L611

Did the compiler warn or something, or how did you find this?

LGTM with CI passing.

error: exception specification in declaration does not match previous declaration
https://godbolt.org/z/6ofjG7xej

[vitalybuka]

rebase

libcxx/include/__verbose_abort

 // Provide a default implementation of __libcpp_verbose_abort if we know that neither the built
 // library nor the user is providing one. Otherwise, just declare it and use the one from the
 // built library or the one provided by the user.
 //
 // We can't provide a great implementation because it needs to be pretty much
 // dependency-free (this is included everywhere else in the library).
 #if defined(_LIBCPP_HAS_NO_VERBOSE_ABORT_IN_LIBRARY) && !defined(_LIBCPP_AVAILABILITY_CUSTOM_VERBOSE_ABORT_PROVIDED)
 
-extern "C" void abort();
-
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 _LIBCPP_NORETURN _LIBCPP_ATTRIBUTE_FORMAT(__printf__, 1, 2) _LIBCPP_HIDE_FROM_ABI inline
 void __libcpp_verbose_abort(const char *, ...) {
-  ::abort();
-  __builtin_unreachable(); // never reached, but needed to tell the compiler that the function never returns
+  __builtin_abort();
 }
 
 _LIBCPP_END_NAMESPACE_STD
 
 #else
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 _LIBCPP_NORETURN _LIBCPP_OVERRIDABLE_FUNC_VIS _LIBCPP_ATTRIBUTE_FORMAT(__printf__, 1, 2)
 void __libcpp_verbose_abort(const char *__format, ...);
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif
 
 #endif // _LIBCPP___VERBOSE_ABORT