[lit] Parse command-line options from LIT_OPTS
Similar to `FILECHECK_OPTS` for FileCheck, `LIT_OPTS` makes it easy to
adjust lit behavior when running the test suite via ninja. For
example:
```
$ LIT_OPTS='--time-tests -vv --filter=threadprivate' \
ninja check-clang-openmp
```
Reviewed By: probinson
Differential Revision: https://reviews.llvm.org/D64135
llvm-svn: 365313
diff --git a/llvm/docs/CommandGuide/lit.rst b/llvm/docs/CommandGuide/lit.rst
index bcaa5c6..7bb499b 100644
--- a/llvm/docs/CommandGuide/lit.rst
+++ b/llvm/docs/CommandGuide/lit.rst
@@ -38,6 +38,11 @@
subset of the options specified on the command line, see
:ref:`selection-options` for more information.
+:program:`lit` parses options from the environment variable ``LIT_OPTS`` after
+parsing options from the command line. ``LIT_OPTS`` is primarily useful for
+supplementing or overriding the command-line options supplied to :program:`lit`
+by ``check`` targets defined by a project's build system.
+
Users interested in the :program:`lit` architecture or designing a
:program:`lit` testing implementation should see :ref:`lit-infrastructure`.