MFC r340361, r345804: catch up on systat in head/

[Neither of these originally mine, but the latter commit referenced
fixes an -fno-common issue and the former is a bugfix]

r340361:
Fix printing of 64-bit counters on 32-bit ppc platforms.

Several statistic counters are uint64_t values and are printed by systat
using %lu. This results in displaying wrong numbers. Use PRIu64 instead.
While there, print variables of size_t using %zd.

r345804:
systat -zarc to display disk activities like -vm

PR: 213310