Add static cast to unsigned char whenever a character classification function is called with a signed char argument, in order to avoid assertions in Windows Debug configuration.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@175006 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Object/COFFObjectFile.cpp

@@ -267,7 +267,7 @@ error_code COFFObjectFile::getSymbolNMTypeChar(DataRefImpl Symb,
   }
 
   if (symb->StorageClass == COFF::IMAGE_SYM_CLASS_EXTERNAL)
-    ret = ::toupper(ret);
+    ret = ::toupper(static_cast<unsigned char>(ret));
 
   Result = ret;
   return object_error::success;