Add getsid system call to bionic

Add getsid() system call to bionic for
all architectures. This is needed for various tools
(e.g. perf).

Adding the getsid system call was done in 3 steps:
() add getsid system call (function name and syscall
number) to libc/SYSCALLS.TXT
() generate all necessary headers by calling
libc/tools/gensyscalls.py. This patch is adding
the generated files since the build system
does not call gensyscalls.py.
() add the system call signature to libc/include/unistd.h

Change-Id: Id69a257e13ec02e1a44085a6b217a3f19ab025b1
Signed-off-by: Irina Tirdea <irina.tirdea@intel.com>