Revert "[lldb] Fix the way we set up the lldb modules infrastructure."

This reverts commit f247725, which was
a re-application of the original change added back in after "fixing" the
underlying issue. See the next commit (also a revert) for more details.

Author: bnbarham

lldb/source/Plugins/ExpressionParser/Clang/ClangModulesDeclVendor.cpp

@@ -670,7 +670,6 @@ ClangModulesDeclVendor::Create(Target &target) {
       arch.GetTriple().str(),
       "-fmodules-validate-system-headers",
       "-Werror=non-modular-include-in-framework-module",
-      "-Xclang=-fincremental-extensions",
       "-Rmodule-build"};
 
   target.GetPlatform()->AddClangModuleCompilationOptions(
@@ -765,6 +764,8 @@ ClangModulesDeclVendor::Create(Target &target) {
                                instance->getFrontendOpts().Inputs[0]))
     return nullptr;
 
+  instance->getPreprocessor().enableIncrementalProcessing();
+
   instance->createASTReader();
 
   instance->createSema(action->getTranslationUnitKind(), nullptr);

lldb/test/API/lang/objc/modules-compile-error/TestModulesCompileError.py

@@ -21,7 +21,7 @@ def test(self):
             "expr @import LLDBTestModule",
             error=True,
             substrs=[
-                "module.h:4:1: error: use of undeclared identifier 'syntax_error_for_lldb_to_find'",
+                "module.h:4:1: error: unknown type name 'syntax_error_for_lldb_to_find'",
                 "syntax_error_for_lldb_to_find // comment that tests source printing",
                 "could not build module 'LLDBTestModule'",
             ],