Clang: Change temporary directory for clangbackend

This is meant to

  1. Work around a libclang bug on Windows (not deleting preamble files)
  2. Delete left-over preamble files in case of a clangbackend crash

The temporary diretory will be removed on Qt Creator exit.

Task-number: QTCREATORBUG-10988
Change-Id: Ia5837c2a6ab2d55366d167dd591d87faaededf3e
Reviewed-by: Marco Bubke <marco.bubke@theqtcompany.com>
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@theqtcompany.com>

src/libs/clangbackendipc/connectionclient.h

@@ -35,6 +35,7 @@
 #include "lineprefixer.h"
 
 #include <QLocalSocket>
+#include <QProcessEnvironment>
 
 #include <memory>
 
@@ -100,6 +101,8 @@ private:
 
     void ensureMessageIsWritten();
 
+    QProcessEnvironment processEnvironment() const;
+
 private:
     mutable std::unique_ptr<QProcess> process_;
     QLocalSocket localSocket;