Revert "Clang: Merge channels from clangbackend on Windows"

This reverts commit 179d8dce73.

It causes random crashes caused by different QProcesses so revert
until we find a solution for that.

Change-Id: Id42f996f54aa5926191f02f9b881ba72eb94689e
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@qt.io>

src/libs/clangsupport/processcreator.cpp

@@ -36,13 +36,6 @@ namespace ClangBackEnd {
 
 using namespace std::chrono_literals;
 
-static QProcess::ProcessChannelMode kProcessChannelMode
-#ifdef Q_OS_WIN
-    = QProcess::MergedChannels;
-#else
-    = QProcess::ForwardedChannels;
-#endif
-
 ProcessCreator::ProcessCreator()
 {
 }
@@ -73,7 +66,7 @@ std::future<QProcessUniquePointer> ProcessCreator::createProcess() const
     return std::async(std::launch::async, [&] {
         checkIfProcessPathExists();
         auto process = QProcessUniquePointer(new QProcess);
-        process->setProcessChannelMode(kProcessChannelMode);
+        process->setProcessChannelMode(QProcess::QProcess::ForwardedChannels);
         process->setProcessEnvironment(processEnvironment());
         process->start(m_processPath, m_arguments);
         process->waitForStarted(5000);