This will enable GCC to compile JNI libraries with -fwhole-program.

http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html

Of course is possible for the library developer to mark JNI functions as externally_visible themselves. However I can't think of a case where a library developer would want to declare a function as JNIEXPORT and not make it externally visible. If JNIEXPORT already tagged these functions as external then we'd be enabling optimization of JNI libraries with minimal effort for the library developer. Of course GCC's behavior would not change unless the linker was run with -fwhole-program.

It might be necessary to wrap this setting of JNIEXPORT in #ifdef __GNUC__ in order to support other compilers.