This fixes the following warning on Windows with latest Clang:
```
[160/3057] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/Signals.cpp.obj
In file included from C:/git/llvm-project/llvm/lib/Support/Signals.cpp:260:
C:/git/llvm-project/llvm/lib/Support/Windows/Signals.inc(834,15): warning: comparison of integers of different signs: 'int' and 'unsigned int' [-Wsign-compare]
if (RetCode == (0xE0000000 | EX_IOERR))
~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~
1 warning generated.```
//
// 0xE0000000 is combined with the return code in the exception raised in
// CrashRecoveryContext::HandleExit().
- int RetCode = (int)EP->ExceptionRecord->ExceptionCode;
+ unsigned RetCode = EP->ExceptionRecord->ExceptionCode;
if (RetCode == (0xE0000000 | EX_IOERR))
return;
LLVMUnhandledExceptionFilter(EP);