nios2: Fix printf size_t format related warnings (again...)

nios2: Fix printf size_t format related warnings (again...)

When compiling the current code on GCC 4.8.3, the following warnings
appear:

warning: format '%zu' expects argument of type 'size_t', but argument
2 has type 'long unsigned int' [-Wformat=]

There were many mails about such warnings on different architectures.
This patch limits itself to the nios2 architecture.

The problem is that for the size_t (%zu, %zd, ...) arguments of
printf GCC does not verify the type match to size_t type. It verifies
the type match to the compiler-defined __SIZE_TYPE__ type. Thus, if
size_t is defined different from __SIZE_TYPE__ - warnings inevitably
appear.

There is a comment by Thomas Chou to the (rejected) patch:
http://patchwork.ozlabs.org/patch/272102/
which explains that the older GCC toolchains (gcc-3.4.6 and gcc-4.1.2)
expect size_t to be "unsigned long" and the newer expect it to be
"unsigned int". Thus, no matter how we define size_t - either way
warnings appear when using some GCC version.

By rejecting that patch, a choice was made to prefer older GCC versions
and leave the warnings when building with the newer toolchains.
Personally, I disagree with this choice...

In any case, this patch proposes a way to fix the warnings for any GCC
version. Just define size_t using the __SIZE_TYPE__ compiler-defined
type and the type verification will pass.

I tested that this fixes the warning on GCC 4.8.3. I don't have an
older toolchain to test with, but __SIZE_TYPE__ was definitely defined
in GCC 3.4.6, so it should work there too.

Signed-off-by: Vasili Galka <vvv444@gmail.com>
Signed-off-by: Thomas Chou <thomas@wytron.com.tw>