arc: Fix printf size_t format related warnings (again...)

The basic idea: Define size_t using the __SIZE_TYPE__ compiler-defined
type.

For detailed explanation see similar patch for the nios2 arch:
http://patchwork.ozlabs.org/patch/379938/

Signed-off-by: Vasili Galka <vvv444@gmail.com>
Cc: Alexey Brodkin <alexey.brodkin@synopsys.com>

arch/arc/include/asm/posix_types.h

@@ -16,7 +16,11 @@ typedef int			__kernel_pid_t;
 typedef unsigned short		__kernel_ipc_pid_t;
 typedef unsigned short		__kernel_uid_t;
 typedef unsigned short		__kernel_gid_t;
+#ifdef __GNUC__
+typedef __SIZE_TYPE__		__kernel_size_t;
+#else
 typedef unsigned int		__kernel_size_t;
+#endif
 typedef int			__kernel_ssize_t;
 typedef int			__kernel_ptrdiff_t;
 typedef long			__kernel_time_t;