Merge bitcoin/bitcoin#27449: doc: update OpenBSD build docs for 7.3 (external signer support available)

6b17994ede6fe1961667d2e96127291b2a8b4f9d doc: update OpenBSD build docs for 7.3 (external signer support available) (Sebastian Falbesoner)

Pull request description:

  With OpenBSD 7.3, the waitid(2) system call is implemented (see openbsd/src@8112871, first mentioned kernel improvement at https://www.openbsd.org/73.html).

  This means Boost.Process finally doesn't fail to compile anymore and we can remove the build hint about missing external signer support. Tested on my amd64 machine by reconfiguring / rebuilding master branch and successfully running the functional test wallet_signer.py. ✔️

ACKs for top commit:
  fanquake:
    ACK 6b17994ede6fe1961667d2e96127291b2a8b4f9d - haven't tested, but looks good to me.

Tree-SHA512: 5bbcecce4ced38d8221f2c906a54667e50317e9ded182554cf73bb7f2fce55a38e53730eca25f813cff1d2d65c94141eb158d40f83228d12dcf859c16a1798b9

Author: fanquake

doc/build-openbsd.md

@@ -1,6 +1,6 @@
 # OpenBSD Build Guide
 
-**Updated for OpenBSD [7.1](https://www.openbsd.org/71.html)**
+**Updated for OpenBSD [7.3](https://www.openbsd.org/73.html)**
 
 This guide describes how to build dashd, command-line utilities, and GUI on OpenBSD.
 
@@ -82,10 +82,6 @@ export AUTOMAKE_VERSION=1.16
 
 ### 1. Configuration
 
-Note that external signer support is currently not available on OpenBSD, since
-the used header-only library Boost.Process fails to compile (certain system
-calls and preprocessor defines like `waitid()` and `WEXITED` are missing).
-
 There are many ways to configure Dash Core, here are a few common examples:
 
 ##### Descriptor Wallet and GUI: