Merge pull request #23935 from slavapestov/re-enable-tests

Re-enable tests with 'REQUIRES: shell'
diff --git a/test/lit.cfg b/test/lit.cfg
index 945a8b6..b6cd795 100644
--- a/test/lit.cfg
+++ b/test/lit.cfg
@@ -170,9 +170,12 @@
 
 # Choose between lit's internal shell pipeline runner and a real shell.  If
 # LIT_USE_INTERNAL_SHELL is in the environment, we use that as an override.
-use_lit_shell = os.environ.get('LIT_USE_INTERNAL_SHELL', not kIsWindows)
+use_lit_shell = os.environ.get('LIT_USE_INTERNAL_SHELL', kIsWindows)
+if not use_lit_shell:
+    config.available_features.add('shell')
+
 config.test_format = swift_test.SwiftTest(coverage_mode=config.coverage_mode,
-                                          execute_external=use_lit_shell)
+                                          execute_external=not use_lit_shell)
 
 # suffixes: A list of file extensions to treat as test files.
 config.suffixes = ['.swift', '.ll', '.sil', '.gyb', '.m', '.swiftinterface',