Fix build on NetBSD

Do not rely on int8_t (and friends) not being preprocessor
 symbols (or symbols expanding to themselves). On NetBSD (for example) the
 glue(u, SDATA_TYPE) results in u__int8_t, which is undefined. There is no way
 to stop cpp expanding inner macros, so just add the few lines explicitly and
 get rid of the magic.

Signed-off-by: Martin Husemann <martin@NetBSD.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

This commit is a backport from: https://github.com/qemu/qemu/commit/dc9a353cf7de78b9fae3e46410803d487fd2fc8f