#18 patch to allow enable support for building as a dll

[Ebben]

I have modified the FBCALL definition to include the necessary declspec info for using a dll version of the rtlib when passing certain defines to the compiler.

The only modified file is src/rtlib/fb.h changes start @ line 217:

*** Begin Code ***

ifndef FBCALL

#if defined (BUILD_DLL)
    #if defined (TARGET_WIN32)  
        #define FBCALL __declspec(dllexport)
    #elif defined (TARGET_LINUX)
        #define FBCALL
    #else
        #error "Unsupported platform"
    #endif
#elif defined (USE_DLL)
    #if defined (TARGET_WIN32)
        #define FBCALL __declspec(dllimport)
    #elif defined (TARGET_LINUX)
        #define FBCALL
    #else
        #error "Unsupported platform"
    #endif
#else
    #define FBCALL
#endif

endif / !defined FBCALL /

*** END CODE ***

This patch only adds the declspec info for WIN32, it doesn't alter the makefile at all. I tested it with a simple manual build and it some portions of the code will need some work for the lib to link.