[clang][test] Use opt -passes=<name> instead of opt -name

Updated the RUN line in several test cases to use the new PM syntax
  opt -passes=<pipeline>
instead of the deprecated syntax
  opt -pass1 -pass2

This was not a complete cleanup in clang/test. But just a swipe using
some simple search-and-replace. Mainly for RUN lines involving
-mem2reg, -instnamer and -early-cse.