Disable SwiftDWARFImporterDelegate by default.

rdar://problem/56582727

Author: adrian-prantl

lldb/lit/Swift/No.swiftmodule-ObjC.test

@@ -11,6 +11,7 @@
 # RUN: %target-swiftc -o %t/a.out %t/main.o %t/ObjCStuff.o
 # RUN: %lldb %t/a.out -s %s | FileCheck %S/Inputs/No.swiftmodule-ObjC.swift
 
+settings set symbols.use-swift-dwarfimporter true
 breakpoint set -p "break here"
 run
 frame variable -d no-dynamic

lldb/source/Core/CoreProperties.td

@@ -10,7 +10,7 @@ let Definition = "modulelist" in {
     DefaultStringValue<"">,
     Desc<"The path to the clang modules cache directory (-fmodules-cache-path).">;
   def UseDWARFImporter: Property<"use-swift-dwarfimporter", "Boolean">,
-    DefaultTrue,
+    DefaultFalse,
     Desc<"Reconstruct Clang module dependencies from DWARF when debugging Swift code">;
   def SwiftModuleLoadingMode: Property<"swift-module-loading-mode", "Enum">,
     DefaultEnumValue<"eSwiftModuleLoadingModePreferSerialized">,