Add LLVM libcxxabi (#1063)

* third_party: Add libcxxabi

Added libcxxabi from LLVM 17.0.6
The library implements the Itanium C++ exception handling ABI.

* third_party/libcxxabi: Enable __cxa_thread_atexit

Enable `__cxa_thread_atexit` from libcxxabi.
`__cxa_thread_atexit_impl` is still implemented by the cosmo libc.
The original `__cxa_thread_atexit` has been removed.

* third_party/libcxx: Build with exceptions

Build libcxx with exceptions enabled.

- Removed `_LIBCPP_NO_EXCEPTIONS` from `__config`.
- Switched the exception implementation to `libcxxabi`. These two files
are taken from the same `libcxx` version as mentioned in `README.cosmo`.
- Removed `new_handler_fallback` in favor of `libcxxabi` implementation.
- Enable `-fexceptions` and `-frtti` for `libcxx`.
- Removed `THIRD_PARTY_LIBCXX` dependency from `libcxxabi` and
`libunwind`. These libraries do not use any runtime `libcxx` functions,
just headers.

* libc: Remove remaining redundant cxa functions

- `__cxa_pure_virtual` in `libcxxabi` is also a stub similar to the
existing one.
- `__cxa_guard_*` from `libcxxabi` is used instead of the ones from
Android.

Now there should be no more duplicate implementations.
`__cxa_thread_atexit_impl`, `__cxa_atexit`, and related supporting
functions, are still left to other libraries as in `libcxxabi`.

`libcxxabi` is also now added to `cosmopolitan.a` to make up for the
removed functions.

Affected in-tree libraries (`third_party/double-conversion`) have been
updated.

third_party/libcxxabi/abort_message.cc

@@ -0,0 +1,79 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "libc/isystem/stdlib.h"
+#include "libc/stdio/stdio.h"
+#include "libc/isystem/stdarg.h"
+#include "third_party/libcxxabi/abort_message.h"
+
+#ifdef __BIONIC__
+#   include <android/api-level.h>
+#   if __ANDROID_API__ >= 21
+#       include <syslog.h>
+        extern "C" void android_set_abort_message(const char* msg);
+#   else
+#       include <assert.h>
+#   endif // __ANDROID_API__ >= 21
+#endif // __BIONIC__
+
+#if defined(__APPLE__) && __has_include(<CrashReporterClient.h>)
+#   include <CrashReporterClient.h>
+#   define _LIBCXXABI_USE_CRASHREPORTER_CLIENT
+#endif
+
+void abort_message(const char* format, ...)
+{
+    // Write message to stderr. We do this before formatting into a
+    // variable-size buffer so that we still get some information if
+    // formatting into the variable-sized buffer fails.
+#if !defined(NDEBUG) || !defined(LIBCXXABI_BAREMETAL)
+    {
+        fprintf(stderr, "libc++abi: ");
+        va_list list;
+        va_start(list, format);
+        vfprintf(stderr, format, list);
+        va_end(list);
+        fprintf(stderr, "\n");
+    }
+#endif
+
+    // Format the arguments into an allocated buffer. We leak the buffer on
+    // purpose, since we're about to abort() anyway.
+#if defined(_LIBCXXABI_USE_CRASHREPORTER_CLIENT)
+    char* buffer;
+    va_list list;
+    va_start(list, format);
+    vasprintf(&buffer, format, list);
+    va_end(list);
+
+    CRSetCrashLogMessage(buffer);
+#elif defined(__BIONIC__)
+    char* buffer;
+    va_list list;
+    va_start(list, format);
+    vasprintf(&buffer, format, list);
+    va_end(list);
+
+#   if __ANDROID_API__ >= 21
+    // Show error in tombstone.
+    android_set_abort_message(buffer);
+
+    // Show error in logcat.
+    openlog("libc++abi", 0, 0);
+    syslog(LOG_CRIT, "%s", buffer);
+    closelog();
+#   else
+    // The good error reporting wasn't available in Android until L. Since we're
+    // about to abort anyway, just call __assert2, which will log _somewhere_
+    // (tombstone and/or logcat) in older releases.
+    __assert2(__FILE__, __LINE__, __func__, buffer);
+#   endif // __ANDROID_API__ >= 21
+#endif // __BIONIC__
+
+    abort();
+}