shutdown () function causes undefined symbol error with 2.0.13

[vargaz]

Testcase:

#include <sys/socket.h>

void main ()
{
	shutdown (0, 0);
}

To reproduce: emcc bug.c
Expected result: compiles
Actual result:

error: undefined symbol: __sys_shutdown (referenced by top-level compiled C/C++ code)
warning: Link with `-s LLD_REPORT_UNDEFINED` to get more information on undefined symbols
warning: To disable errors for undefined symbols use `-s ERROR_ON_UNDEFINED_SYMBOLS=0`
warning: ___sys_shutdown may need to be added to EXPORTED_FUNCTIONS if it arrives from a system library
Error: Aborting compilation due to previous errors

Probably caused by: d7c7aed

[sbc100]

I don't think we ever actually had an implementation of this but #13399 should restore the previous behavior which is to return ENOSYS from shutdown.