tools: build wrpc-dump with "-m32" flag (well, we assume PC host)

This fixes the problem with data sizes when building on a 64-bit host.
Now the dump of ppi makes sense, besides endianness.

Please note how this requires a cross-compile environment for i386
when you build on x86-64. Later on this requirement is lifted.
Signed-off-by: Alessandro Rubini <rubini@gnudd.com>