Utils: Re-do Replace SynchronousCommand::flags by a named bool

The potential extensibility was never used, and a similar use case
in QtcProcess (setLowPriority()) used a named setter.

Change-Id: I87d84ea2206995d5069265f8df78f40cf2ba8a36
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/cmakeprojectmanager/cmakeprojectimporter.cpp

@@ -200,7 +200,7 @@ static FilePath qmakeFromCMakeCache(const CMakeConfig &config)
 
     SynchronousProcess cmake;
     cmake.setTimeoutS(5);
-    cmake.setFlags(SynchronousProcess::UnixTerminalDisabled);
+    cmake.setDisableUnixTerminal();
     Environment env = Environment::systemEnvironment();
     Environment::setupEnglishOutput(&env);
     cmake.setEnvironment(env);