fiptool: Enable Visual Studio build ...

Updates are required to enable the fiptool utility to be built on a
Windows platform.  This change modifies the source files to enable
building with Visual Studio (detected via preprocessor settings).
The primary changes are:
  1.  Provide an implementation of the getopt_long function.  This does
      not exist in the Visual Studio CRT libraries because Windows
      commands normally use '/' not '-' as an option indicator.
  2.  Redirect some function names to match those supported by the
      Visual Studio libraries (when building with Visual Studio).
  2.  Modify a structure name (stat) to match that provided
      by the Visual Studio libraries (_stat).

Note - this change does not provide makefile updates.  It only modifies
       the sources to enable the fiptool to be built from a Visual
       Studio project.  In normal use the presence of FIPTOOL.EXE is
       enough to satisfy the make requirements.  A makefile change may
       be derived from the Visual Studio command line information at
       some point in the future.

Change-Id: I3ade77ea140246af3c030920b3f97c070087f111
Signed-off-by: Evan Lloyd <evan.lloyd@arm.com>