stdlib: silence truncation warning on Windows

The returned type `std::streamoff` on Windows x64 is a `long long`
rather than `int`.  This results in a 64-to-32 bit shortening of the
value.  Use the appropriate type to avoid the truncation.

`strlen` returns a unsigned value, but `std::streamoff` is an signed
value.  Explicitly cast the value to avoid the warning about the
implicit signed conversion.

Author: compnerd

stdlib/public/stubs/Stubs.cpp

@@ -473,9 +473,9 @@ static const char *_swift_stdlib_strtoX_clocale_impl(
   ValueStream >> ParsedValue;
   *outResult = ParsedValue;
 
-  int pos = ValueStream.tellg();
+  std::streamoff pos = ValueStream.tellg();
   if (ValueStream.eof())
-    pos = strlen(nptr);
+    pos = static_cast<std::streamoff>(strlen(nptr));
   if (pos <= 0)
     return nullptr;