[SVE] Add checks for no warnings in SVE tests

There are now quite a few SVE tests in LLVM and Clang that do not
emit warnings related to invalid use of EVT::getVectorNumElements()
and VectorType::getNumElements(). For these tests I have added
additional checks that there are no warnings in order to prevent
any future regressions.

Differential Revision: https://reviews.llvm.org/D80712