Merge bitcoin/bitcoin#34182: doc: Update OpenBSD Build Guide

84d8c52662 doc: Update OpenBSD Build Guide (Hennadii Stepanov)

Pull request description:

  [OpenBSD 7.8](https://www.openbsd.org/78.html) ships LLVM/Clang 19.1.7, which satisfies the recently [updated](https://github.com/bitcoin/bitcoin/pull/33555) minimum requirement.

ACKs for top commit:
  katesalazar:
    ACK https://github.com/bitcoin/bitcoin/commit/84d8c52662545b33c0d02c8ac02ae694950ad9d4
  janb84:
    ACK 84d8c52662

Tree-SHA512: 06644733702d72687a2e860cf561c9ca39a3cf1d7c339c94f2b87d36b530776f7e7d0f7e3d22cd858ee8639bd4e85c47081602cbe829c7406cdcd65380e84130

doc/build-openbsd.md

@@ -1,6 +1,6 @@
 # OpenBSD Build Guide
 
-**Updated for OpenBSD [7.6](https://www.openbsd.org/76.html)**
+**Updated for OpenBSD [7.8](https://www.openbsd.org/78.html)**
 
 This guide describes how to build bitcoind, command-line utilities, and GUI on OpenBSD.
 
@@ -21,8 +21,11 @@ pkg_add sqlite3
 
 To build Bitcoin Core without the wallet, use `-DENABLE_WALLET=OFF`.
 
-Cap'n Proto is needed for IPC functionality (see [multiprocess.md](multiprocess.md))
-and can be built from source: https://capnproto.org/install.html
+Cap'n Proto is needed for IPC functionality (see [multiprocess.md](multiprocess.md)):
+
+```bash
+pkg_add capnproto
+```
 
 Compile with `-DENABLE_IPC=OFF` if you do not need IPC functionality.