devel/uv: fix build on armv7

A type error that pops up on armv7.
As subsec_nanos() is in the range 0 to 1e9, it always fits into an i32
either way, so "as" is sufficient for a conversion.

Also enable on i386, where this port now builds fine.

Approved by: portmgr (build fix blanket)
See also: https://github.com/astral-sh/tokio-tar/issues/100
MFH: 2026Q3

(cherry picked from commit f0cedef322bd5f59f4047d186e99657c1edda3f4)