libcflat: add PRI(dux)32 format types

So we can have portable formatting of uint32_t types. However there is
a catch. Different compilers can use legally subtly different types
though so we need to probe the compiler defined intdef.h first.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>