games/nethack36: fix build on GCC architectures

Use C11 compiler:
In file included from ../include/isaac64.h:4,

from isaac64.c:17:

../include/integer.h:88: error: conflicting types for 'int64_t'
/usr/include/sys/_stdint.h:51: error: previous declaration of 'int64_t' was here
../include/integer.h:89: error: conflicting types for 'uint64_t'
/usr/include/sys/_stdint.h:71: error: previous declaration of 'uint64_t' was here

Approved by: mentors (implicit approval)