Add a demangler option to hide the "__C" module name.

This part of a series of patches to bring ASTPrinter and Swift Demangler to
feature parity, which is needed by LLDB, which depends on using the strings
produced by either interchangibly.

rdar://problem/63700540

Author: adrian-prantl

include/swift/Demangling/Demangle.h

@@ -58,6 +58,7 @@ struct DemangleOptions {
   bool ShowFunctionArgumentTypes = true;
   bool DisplayDebuggerGeneratedModule = true;
   bool DisplayStdlibModule = true;
+  bool DisplayObjCModule = true;
   std::function<std::string(uint64_t, uint64_t)> GenericParameterName =
       genericParameterName;
 

lib/Demangling/NodePrinter.cpp

@@ -246,6 +246,8 @@ class NodePrinter {
     if (Context->getKind() == Node::Kind::Module) {
       if (Context->getText() == swift::STDLIB_NAME)
         return Options.DisplayStdlibModule;
+      if (Context->getText() == swift::MANGLING_MODULE_OBJC)
+        return Options.DisplayObjCModule;
       if (Context->getText().startswith(LLDB_EXPRESSIONS_MODULE_NAME_PREFIX))
         return Options.DisplayDebuggerGeneratedModule;
     }

test/Demangle/demangle-special-options.test

@@ -2,3 +2,8 @@ RUN: swift-demangle -display-stdlib-module=true sSi | %FileCheck %s --check-pref
 SWIFT-INT: {{ Swift.Int$}}
 RUN: swift-demangle -display-stdlib-module=false sSi | %FileCheck %s --check-prefix=INT
 INT: {{ Int$}}
+
+RUN: swift-demangle -display-objc-module=true sSo6CGRectVD | %FileCheck %s --check-prefix=OBJC-CGRECT
+OBJC-CGRECT: {{ __C.CGRect$}}
+RUN: swift-demangle -display-objc-module=false sSo6CGRectVD | %FileCheck %s --check-prefix=CGRECT
+CGRECT: {{ CGRect$}}

tools/swift-demangle/swift-demangle.cpp

@@ -80,6 +80,11 @@ static llvm::cl::opt<bool> DisplayStdlibModule(
     "display-stdlib-module", llvm::cl::init(true),
     llvm::cl::desc("Qualify types originating from the Swift standard library"),
     llvm::cl::Hidden);
+
+static llvm::cl::opt<bool> DisplayObjCModule(
+    "display-objc-module", llvm::cl::init(true),
+    llvm::cl::desc("Qualify types originating from the __ObjC module"),
+    llvm::cl::Hidden);
 /// \}
 
 
@@ -243,6 +248,7 @@ int main(int argc, char **argv) {
   if (Simplified)
     options = swift::Demangle::DemangleOptions::SimplifiedUIDemangleOptions();
   options.DisplayStdlibModule = DisplayStdlibModule;
+  options.DisplayObjCModule = DisplayObjCModule;
 
   if (InputNames.empty()) {
     CompactMode = true;