mksysinfo: force Passwd.Pw_[ug]id from int32 to uint32
mksysinfo: force Passwd.Pw_[ug]id from int32 to uint32

Solaris 10 uses int32 for the Pw_uid and Pw_gid fields of Passwd,
but most systems, including Solaris 11, use uint32.  Force uint32
for consistency and to fix the build.

Change-Id: I1cc75afa28e13d30180182edfc574ff35556dd45
Reviewed-on: https://go-review.googlesource.com/88195
Reviewed-by: Than McIntosh <4b2922593166fc595a9b1a408f34f5d3817fe9d2@google.com>

golang/gofrontend,golang/gofrontend,golang/gofrontend,golang/gofrontend