Fix windows xp compile error,  C4013 and C2065

build ffi.dll in windows xp(sp2), with VS2005 prompt command tool, error info as below:

ffi.c(2962) : error c2220 warning treated as error - no 'object' file generated
ffi.c(2962) : warning C4013: “GetModuleHandleExA” undefined assuming extern returning int
ffi.c(2962) : error C2065: “GET_MODULE_HANDLE_EX_FLAG_FROM_ADDRESS”: undeclared identifier

refer to: https://github.com/jmckaskill/luaffi/issues/55