Clang: forward clangbackend QDebug messages to stdout

...to see them in both qtcreator application output
and DebugView.
clangbackend is a separate process which provides
QtCreator stdout and stderr channels so we need to
have QDebug messages there in order to receive them.

Change-Id: I2edc4de1ca203b061395b0b3070e4471348eaad7
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@qt.io>

src/tools/clangbackend/clangbackendmain.cpp

@@ -33,6 +33,8 @@
 #include <clangcodemodelserver.h>
 #include <clangcodemodelclientproxy.h>
 
+#include <iostream>
+
 using ClangBackEnd::ClangCodeModelClientProxy;
 using ClangBackEnd::ClangCodeModelServer;
 using ClangBackEnd::ConnectionServer;
@@ -53,8 +55,20 @@ QString processArguments(QCoreApplication &application)
     return parser.positionalArguments().first();
 }
 
+#ifdef Q_OS_WIN
+static void messageOutput(QtMsgType type, const QMessageLogContext &, const QString &msg)
+{
+    std::wcout << msg.toStdWString() << std::endl;
+    if (type == QtFatalMsg)
+        abort();
+}
+#endif
+
 int main(int argc, char *argv[])
 {
+#ifdef Q_OS_WIN
+    qInstallMessageHandler(messageOutput);
+#endif
     QLoggingCategory::setFilterRules(QStringLiteral("qtc.*.debug=false"));
 
     QCoreApplication::setOrganizationName(QStringLiteral("QtProject"));