[BatchMode] <rdar://40526328> Add a testcase for signal-interruption of cancelled batch constituents.

Author: graydon

test/Driver/batch_mode_parseable_output_cancellation.swift

@@ -0,0 +1,14 @@
+// RUN: %empty-directory(%t)
+// RUN: touch %t/file-01.swift
+// RUN: echo 'public func main() { help_an_error_happened() }' >%t/main.swift
+//
+// RUN: not %swiftc_driver -enable-batch-mode -parseable-output -serialize-diagnostics -c -emit-module -module-name main -j 1 %t/file-01.swift %t/main.swift 2>&1 | %FileCheck %s
+//
+//      CHECK:   "kind": "signalled",
+// CHECK-NEXT:   "name": "compile",
+// CHECK-NEXT:   "pid": -{{[1-9][0-9]*}},
+// CHECK-NEXT:   "process": {
+// CHECK-NEXT:   	"real_pid": {{[1-9][0-9]*}}
+// CHECK-NEXT:   },
+// CHECK-NEXT:   "error-message": "{{.*}}",
+// CHECK-NEXT:   "signal": 2