Merge remote-tracking branch 'origin/master' into master-next

Author: swift-ci

test/lit.cfg

@@ -170,9 +170,12 @@ kIsWindows = platform.system() == 'Windows'
 
 # 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',