Make sure to setup the language defaults normally when outputting a PCH.

include/cling/Interpreter/InvocationOptions.h

@@ -13,6 +13,10 @@
 #include <string>
 #include <vector>
 
+namespace clang {
+  class LangOptions;
+};
+
 namespace cling {
 
   ///\brief Class that stores options that are used by both cling and
@@ -42,7 +46,7 @@ namespace cling {
     /// or './cling -x c') that this shouldn't be done.  This will return false
     /// in those cases.
     ///
-    bool DefaultLanguage() const { return !Language && !StdVersion; }
+    bool DefaultLanguage(const clang::LangOptions&) const;
 
     unsigned Language : 1;
     unsigned ResourceDir : 1;

lib/Interpreter/CIFactory.cpp

@@ -421,7 +421,7 @@ namespace {
     Opts.FastMath = 1;
 #endif
 
-    if (CompilerOpts.DefaultLanguage()) {
+    if (CompilerOpts.DefaultLanguage(Opts)) {
 #ifdef __STRICT_ANSI__
       Opts.GNUMode = 0;
 #else
@@ -445,7 +445,7 @@ namespace {
       Opts.MicrosoftExt = 0;
     }
 
-    if (CompilerOpts.DefaultLanguage()) {
+    if (CompilerOpts.DefaultLanguage(Opts)) {
 #if _GLIBCXX_USE_FLOAT128
       // We are compiling with libstdc++ with __float128 enabled.
       if (!Target.hasFloat128Type()) {

lib/Interpreter/InvocationOptions.cpp

@@ -11,6 +11,7 @@
 #include "cling/Interpreter/ClingOptions.h"
 #include "cling/Utils/Output.h"
 
+#include "clang/Basic/LangOptions.h"
 #include "clang/Driver/Options.h"
 
 #include "llvm/Option/Arg.h"
@@ -144,6 +145,20 @@ void CompilerOptions::Parse(int argc, const char* const argv[],
   }
 }
 
+bool CompilerOptions::DefaultLanguage(const LangOptions& LangOpts) const {
+  // When StdVersion is set (-std=c++11, -std=gnu++11, etc.) then definitely
+  // don't setup the defaults, as they may interfere with what the user is doing
+  if (StdVersion)
+    return false;
+
+  // Also don't set up the defaults when language is explicitly set; unless
+  // the language was set to generate a PCH, in which case definitely do.
+  if (Language)
+    return LangOpts.CompilingPCH || HasOutput;
+
+  return true;
+}
+
 InvocationOptions::InvocationOptions(int argc, const char* const* argv) :
   MetaString("."), ErrorOut(false), NoLogo(false), ShowVersion(false),
   Help(false), NoRuntime(false) {