Utility.FileIO: set close-on-exec flag for all functions

Utility.FileIO: set close-on-exec flag for all functions

Utility.FileIO.CloseOnExec is largely copied from
System.File.OsPath.Internal with the simple modification of
setting the flag.

Unfortunately, openTempFile does not set the flag when
opening the file, but afterwards, leaving it vulnerable to a race.
A lot of code, including posix and windows specific code,
would need to be copied from file-io in order to fix that.
Still, I consider this implementation a placeholder, it doesn't truely
fix all instances of the problem.

I hope that this will be addressed in file-io itself, see
https://github.com/haskell/file-io/issues/44

Utility.FileIO.CloseOnExec could form the basis of a
file-io-closeonexec library, depending on how things go with that
issue.

Sponsored-by: the NIH-funded NICEMAN (ReproNim TR&D3) project