On OpenBSD amd64 memory stats are missing the buffer cache info

[cjeker]

Host operating system: output of uname -a

OpenBSD motoko.zyd.ch 6.8 GENERIC.MP#297 amd64

node_exporter version: output of node_exporter --version

node_exporter, version 1.1.1 (branch: master, revision: 41c003d)
build user: me
build date: 20210215-13:38:40
go version: go1.15.7
platform: openbsd/amd64

node_exporter command line flags

no command line flags

Are you running node_exporter in Docker?

No

What did you do that produced an error?

Since the switch for OpenBSD amd64 to not use cgo the memory info lacks correct cache memory info.
The non-amd64 specific version does the right thing but needs cgo. The cache info is not part of struct uvmexp.

What did you expect to see?

HELP node_memory_cache_bytes Memory information field cache_bytes.

TYPE node_memory_cache_bytes gauge

node_memory_cache_bytes 5.822767104e+09

What did you see instead?

HELP node_memory_cache_bytes Memory information field cache_bytes.

TYPE node_memory_cache_bytes gauge

node_memory_cache_bytes 0