[FileCheck] Don't propagate `FILECHECK_DUMP_INPUT_ON_FAILURE` and
`FILECHECK_OPTS` into environment for FileCheck tests.


This fixes the following FileCheck tests:

* FileCheck/dump-input-enable.txt
* FileCheck/match-full-lines.txt

when `FILECHECK_DUMP_INPUT_ON_FAILURE` is set in the environment.

By default llvm-lit propagates `FILECHECK_DUMP_INPUT_ON_FAILURE` and
`FILECHECK_OPTS` from llvm-lit's environment into the test environment.
Unfortunately this can break FileCheck's tests because they expect that
these environment variables not to be set.


Reviewers: jdenny, probinson, george.karpenkov

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D56541

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@350850 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/FileCheck/lit.local.cfg b/test/FileCheck/lit.local.cfg
new file mode 100644
index 0000000..307da45
--- /dev/null
+++ b/test/FileCheck/lit.local.cfg
@@ -0,0 +1,13 @@
+# Unset environment variables that the FileCheck tests
+# expect not to be set.
+file_check_expected_unset_vars = [
+for env_var in file_check_expected_unset_vars:
+  if env_var in config.environment:
+    lit_config.note('Removing {} from environment for FileCheck tests'.format(
+      env_var)
+    )
+    config.environment.pop(env_var)