[NFC] Use stdin for some tests instead of positional argument.

Summary: Otherwise unexpected matches with the path to the tests might happen.

Reviewers: rengolin, spatel, efriedma, RKSimon

Reviewed By: spatel

Subscribers: n.bozhenov, javed.absar, llvm-commits

Patch by Andrei Elovikov <andrei.elovikov@intel.com>

Differential Revision: https://reviews.llvm.org/D32994

llvm-svn: 306684