Add support for Linux in Log.output

[oboobortot]

Suggestion for improvement of https://github.com/freeonterminate/delphi/blob/master/FMXLog/FMX.Log.pas method Log.output

If you would like to add support for Linux as well you can use the following

1. Add those units to interface uses clause

uses
  ...
  {$if defined(POSIX)}
  Posix.Unistd,
  Posix.Pthread,
  {$endif}
  ...;

2. Add those lines in the implementation of Log.output class procedure of the class Log in FMX.Log.pas

  {$if defined(LINUX)}
  __write(stderr, OrnamentedText, Length(OrnamentedText));
  __write(stderr, EOL, Length(EOL));
  {$endif}