Give NamedRegionTimer an Enabled flag, allowing all its clients to

switch from this:

  if (TimePassesIsEnabled) {
    NamedRegionTimer T(Name, GroupName);
    do_something();
  } else {
    do_something(); // duplicate the code, this time without a timer!
  }

to this:

  {
    NamedRegionTimer T(Name, GroupName, TimePassesIsEnabled);
    do_something();
  }

llvm-svn: 106285