[libcxxabi] Implement a GCC compatible SEH unwinding personality, __gxx_personality_seh0

[mstorsjo]

Summary

This allows handling SEH based exceptions, with unwind functions provided by libgcc.

[rnk]

lgtm

src/cxa_personality.cpp

 #include <typeinfo>
 
 #include "__cxxabi_config.h"
 #include "cxa_exception.hpp"
 #include "cxa_handlers.hpp"
 #include "private_typeinfo.h"
 #include "unwind.h"
 
+#if defined(__SEH__) && !defined(__USING_SJLJ_EXCEPTIONS__)
+#include <windows.h>
+#include <winnt.h>
+
+extern "C" EXCEPTION_DISPOSITION _GCC_specific_handler(PEXCEPTION_RECORD,
+                                                       void *, PCONTEXT,
+                                                       PDISPATCHER_CONTEXT,
+                                                       _Unwind_Personality_Fn);
+#endif
+
 /*
     Exception Header Layout:
 
 +---------------------------+-----------------------------+---------------+
 | __cxa_exception           | _Unwind_Exception CLNGC++\0 | thrown object |
 +---------------------------+-----------------------------+---------------+
                                                           ^
                                                           |
Else
             1.  A cleanup.
 
         If a cleanup is found
             transfer control to it. return _URC_INSTALL_CONTEXT
         Else a cleanup is not found: return _URC_CONTINUE_UNWIND
 */
 
 #if !defined(_LIBCXXABI_ARM_EHABI)
+#if defined(__SEH__) && !defined(__USING_SJLJ_EXCEPTIONS__)
+static _Unwind_Reason_Code __gxx_personality_imp
+#else
 _LIBCXXABI_FUNC_VIS _Unwind_Reason_Code
 #ifdef __USING_SJLJ_EXCEPTIONS__
 __gxx_personality_sj0
 #else
 __gxx_personality_v0
 #endif
+#endif
                     (int version, _Unwind_Action actions, uint64_t exceptionClass,
                      _Unwind_Exception* unwind_exception, _Unwind_Context* context)
 {
     if (version != 1 || unwind_exception == 0 || context == 0)
         return _URC_FATAL_PHASE1_ERROR;
 
     bool native_exception = (exceptionClass     & get_vendor_and_language) ==
                             (kOurExceptionClass & get_vendor_and_language);
if (actions & _UA_CLEANUP_PHASE)
         // Did not find a cleanup.  Return the results of the scan
         //    (normally _URC_CONTINUE_UNWIND, but could have been _URC_FATAL_PHASE2_ERROR
         //     if we were called improperly).
         return results.reason;
     }
     // We were called improperly: neither a phase 1 or phase 2 search
     return _URC_FATAL_PHASE1_ERROR;
 }
+
+#if defined(__SEH__) && !defined(__USING_SJLJ_EXCEPTIONS__)
+extern "C" EXCEPTION_DISPOSITION
+__gxx_personality_seh0(PEXCEPTION_RECORD ms_exc, void *this_frame,
+                       PCONTEXT ms_orig_context, PDISPATCHER_CONTEXT ms_disp)
+{
+  return _GCC_specific_handler(ms_exc, this_frame, ms_orig_context, ms_disp,
+                               __gxx_personality_imp);
+}
+#endif
+
 #else
 
 extern "C" _Unwind_Reason_Code __gnu_unwind_frame(_Unwind_Exception*,
                                                   _Unwind_Context*);
 
 // Helper function to unwind one frame.
 // ARM EHABI 7.3 and 7.4: If the personality function returns _URC_CONTINUE_UNWIND, the
 // personality routine should update the virtual register set (VRS) according to the