Add UnhandledExceptionHandlerUnix Stub (dotnet/coreclr#8425)

FuncEvalHijack in dbghelpers.S uses UnhandledExceptionHandlerUnix as a
personality routine, but UnhandledExceptionHandlerUnix is not avaiable
for x86 (UnhandledExceptionHandlerUnix is available only when
WIN64EXCEPTIONS which is not defined for x86).

This commit adds UnhandledExceptionHandlerUnix to fix dangling
reference.

Commit migrated from dotnet/coreclr@4e21d57

src/coreclr/src/vm/i386/unixstubs.cpp

@@ -87,6 +87,19 @@ extern "C"
  void STDCALL JIT_ProfilerEnterLeaveTailcallStub(UINT_PTR ProfilerHandle)
  {
  }
+
+ _Unwind_Reason_Code
+ UnhandledExceptionHandlerUnix(
+ IN int version,
+ IN _Unwind_Action action,
+ IN uint64_t exceptionClass,
+ IN struct _Unwind_Exception *exception,
+ IN struct _Unwind_Context *context
+ )
+ {
+ PORTABILITY_ASSERT("UnhandledExceptionHandlerUnix");
+ return _URC_FATAL_PHASE1_ERROR;
+ }
 };
 
 VOID __cdecl PopSEHRecords(LPVOID pTargetSP)