Fix fallback define for DECLSPEC for non-Windows platforms.

Looks like it was a copy/paste error?

GCC doesn't support visibility attributes until gcc4, so just make it blank.

Fixes Bugzilla #2720.

include/begin_code.h

@@ -64,8 +64,6 @@
 # else
 #  if defined(__GNUC__) && __GNUC__ >= 4
 #   define DECLSPEC __attribute__ ((visibility("default")))
-#  elif defined(__GNUC__) && __GNUC__ >= 2
-#   define DECLSPEC __declspec(dllexport)
 #  else
 #   define DECLSPEC
 #  endif