lit's test suite calls lit multiple times for various sample test
suites. `FILECHECK_OPTS` is safe for FileCheck calls in lit's test
suite. It's not safe for FileCheck calls in the sample test suites,
whose output affects the results of lit's test suite.
Without this patch, only one such sample test suite is protected from
`FILECHECK_OPTS`, and currently `shtest-shell.py` breaks with
`FILECHECK_OPTS=-vv`. Moreover, it's hard to predict the future,
especially false passes. Thus, this patch protects all existing and
future sample test suites from `FILECHECK_OPTS` (and the deprecated
`FILECHECK_DUMP_INPUT_ON_FAILURE`).
Reviewed By: probinson
Differential Revision: https://reviews.llvm.org/D65156
7fc52c9da6