allow static linking on Windows

[umlaeute]

it seems that it's impossible to create a dll that statically links against flite.

the problem, is that for static builds you shouldn't export variables with __declspec(dllexport), as found in

flite/include/flite.h

Lines 68 to 73 in 6c9f20d

	#ifdef WIN32
	/* For Visual Studio 2012 global variable definitions */
	#define GLOBALVARDEF __declspec(dllexport)
	#else
	#define GLOBALVARDEF
	#endif

and

flite/src/synth/flite.c

Lines 47 to 52 in 6c9f20d

	#ifdef WIN32
	/* For Visual Studio 2012 global variable definitions */
	#define GLOBALVARDEF __declspec(dllexport)
	#else
	#define GLOBALVARDEF
	#endif

i think the canonical way to handle this is to use a define indicating a static build (and don't use the __declspec(dllexport) decorator if it is set), like so:

#ifdef FLITE_STATIC
# define GLOBALVARDEF 
#else
# ifdef WIN32
/* For Visual Studio 2012 global variable definitions */
#  define GLOBALVARDEF __declspec(dllexport)
# else
#  define GLOBALVARDEF
# endif
#endif

obviously, whoever wants to link flite statically, will then have to define FLITE_STATIC.