When built with ASan, __cxa_throw calls __asan_handle_no_return

[mcgrathr]

Summary

The ASan runtime on many systems intercepts cxa_throw just so it
can call asan_handle_no_return first. Some newer systems such as
Fuchsia don't use interceptors on standard library functions at all,
but instead use sanitizer-instrumented versions of the standard
libraries. When libc++abi is built with ASan, cxa_throw can just
call asan_handle_no_return itself so no interceptor is required.

[phosek]

@EricWF does this look fine to you? I'm happy with this change and I'd like to land it if possible.

[phosek]

LGTM

libcxxabi/trunk/src/cxa_exception.cpp

 #include "cxxabi.h"
 
 #include <exception>        // for std::terminate
 #include <cstring>          // for memset
 #include "cxa_exception.hpp"
 #include "cxa_handlers.hpp"
 #include "fallback_malloc.h"
 
+#if __has_feature(address_sanitizer)
+#include <sanitizer/asan_interface.h>
+#endif
+
 // +---------------------------+-----------------------------+---------------+
 // | __cxa_exception           | _Unwind_Exception CLNGC++\0 | thrown object |
 // +---------------------------+-----------------------------+---------------+
 //                                                           ^
 //                                                           |
 //   +-------------------------------------------------------+
 //   |
 // +---------------------------+-----------------------------+
__cxa_throw(void *thrown_object, std::type_info *tinfo, void (*dest)(void *)) {
     exception_header->terminateHandler  = std::get_terminate();
     exception_header->exceptionType = tinfo;
     exception_header->exceptionDestructor = dest;
     setExceptionClass(&exception_header->unwindHeader);
     exception_header->referenceCount = 1;  // This is a newly allocated exception, no need for thread safety.
     globals->uncaughtExceptions += 1;   // Not atomically, since globals are thread-local
 
     exception_header->unwindHeader.exception_cleanup = exception_cleanup_func;
+
+#if __has_feature(address_sanitizer)
+    // Inform the ASan runtime that now might be a good time to clean stuff up.
+    __asan_handle_no_return();
+#endif
+
 #ifdef __USING_SJLJ_EXCEPTIONS__
     _Unwind_SjLj_RaiseException(&exception_header->unwindHeader);
 #else
     _Unwind_RaiseException(&exception_header->unwindHeader);
 #endif
     //  This only happens when there is no handler, or some unexpected unwinding
     //     error happens.
     failed_throw(exception_header);