avoid sign-conversion-error in erase

[JazzSuite]

Summary

As it is now i ran into this problem: "error: conversion to 'std::size_t' {aka 'long long unsigned int'} from 'long long int' may change the sign of the result [-Werror=sign-conversion]"

[JazzSuite]

as described in summary

llvm/include/llvm/ADT/SmallVector.h

iterator erase(const_iterator CS, const_iterator CE) {
 
     assert(this->isRangeInStorage(S, E) && "Range to erase is out of bounds.");
 
     iterator N = S;
     // Shift all elts down.
     iterator I = std::move(E, this->end(), S);
     // Drop the last elts.
     this->destroy_range(I, this->end());
-    this->set_size(I - this->begin());
+    this->set_size(static_cast<size_type>(I - this->begin()));
     return(N);
   }
 
 private:
   template <class ArgType> iterator insert_one_impl(iterator I, ArgType &&Elt) {
     // Callers ensure that ArgType is derived from T.
     static_assert(
         std::is_same<std::remove_const_t<std::remove_reference_t<ArgType>>,