Reuse ProcessHelper in process launcher

Handle lowPriority and unixTerminalDisabled inside
process launcher.

Change-Id: I7a8998e303da0e79186c1201fc6e1a76edb4e1b3
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

src/libs/utils/processutils.cpp

@@ -24,13 +24,13 @@
 ****************************************************************************/
 
 #include "processutils.h"
-#include <QProcess>
 
 #ifdef Q_OS_WIN
-#ifdef QTCREATOR_PCH_H
-#define CALLBACK WINAPI
-#endif
 #include <qt_windows.h>
+#else
+#include <errno.h>
+#include <stdio.h>
+#include <unistd.h>
 #endif
 
 namespace Utils {
@@ -86,4 +86,21 @@ void ProcessStartHandler::setNativeArguments(QProcess *process, const QString &a
 #endif // Q_OS_WIN
 }
 
+
+void ProcessHelper::setupChildProcess_impl()
+{
+#if defined Q_OS_UNIX
+    // nice value range is -20 to +19 where -20 is highest, 0 default and +19 is lowest
+    if (m_lowPriority) {
+        errno = 0;
+        if (::nice(5) == -1 && errno != 0)
+            perror("Failed to set nice value");
+    }
+
+    // Disable terminal by becoming a session leader.
+    if (m_unixTerminalDisabled)
+        setsid();
+#endif
+}
+
 } // namespace Utils