Merge #13578: [depends, zmq, doc] upgrade zeromq to 4.2.5 and avoid deprecated zeromq api functions

f1bd03eb013b96ff040a8f835e4137fbd2a38cda [depends, zmq, doc] upgrade zeromq to 4.2.5 and avoid deprecated zeromq api functions (mruddy)

Pull request description:

  Upgrade the ZeroMQ dependency from version 4.2.3 to the latest stable version 4.2.5.

  This PR Follows the lead of https://github.com/bitcoin/bitcoin/pull/11986.

  I upgraded both patch files to correspond to the version `4.2.5` libzmq files.
  I assume doing so is still necessary and correct.

  Without updating the patch line numbers, things appear to work, but you get extra log messages while building `depends` because things don't exactly match, e.g.:
  ```
  /bitcoin/depends> make zeromq
  Extracting zeromq...
  /bitcoin/depends/sources/zeromq-4.2.5.tar.gz: OK
  Preprocessing zeromq...
  patching file src/windows.hpp
  Hunk #1 succeeded at 58 (offset 3 lines).
  patching file src/thread.cpp
  Hunk #1 succeeded at 307 with fuzz 2 (offset 87 lines).
  Hunk #2 succeeded at 323 with fuzz 2 (offset 90 lines).
  ```
  Updating the patches seemed cleaner, so I did it. Note that libzmq had some whitespace changes, so that's why the updated patches do too.

  More info: https://github.com/zeromq/libzmq/releases/tag/v4.2.5

  tags: libzmq, zmq, 0mq

Tree-SHA512: 78659dd276b5311e40634b1bbebb802ddd6b69662ba3c84995ef1e3795c49a78b1635112c7fd72a405ea36e2cc3bdeb84e6d00d4e491a349bba1dafff50e2fa5

3 files changed, 7 insertions, 5 deletions

diff --git a/doc/build-unix.md b/doc/build-unix.md
index 337de12b8d..dfeb8ba260 100644
--- a/doc/build-unix.md
+++ b/doc/build-unix.md
@@ -47,7 +47,7 @@ Optional dependencies:
  protobuf    | Payments in GUI  | Data interchange format used for payment protocol (only needed when GUI enabled)
  libqrencode | QR codes in GUI  | Optional for generating QR codes (only needed when GUI enabled)
  univalue    | Utility          | JSON parsing and encoding (bundled version will be used unless --with-system-univalue passed to configure)
- libzmq3     | ZMQ notification | Optional, allows generating ZMQ notifications (requires ZMQ version >= 4.x)
+ libzmq3     | ZMQ notification | Optional, allows generating ZMQ notifications (requires ZMQ version >= 4.0.0)
 
 For the versions used, see [dependencies.md](dependencies.md)
 
@@ -93,7 +93,7 @@ Optional (see --with-miniupnpc and --enable-upnp-default):
 
     sudo apt-get install libminiupnpc-dev
 
-ZMQ dependencies (provides ZMQ API 4.x):
+ZMQ dependencies (provides ZMQ API):
 
     sudo apt-get install libzmq3-dev
 
diff --git a/doc/dependencies.md b/doc/dependencies.md
index 3fc7aecba8..d777aaf66f 100644
--- a/doc/dependencies.md
+++ b/doc/dependencies.md
@@ -26,5 +26,5 @@ These are the dependencies currently used by Bitcoin Core. You can find instruct
 | Qt | [5.9.6](https://download.qt.io/official_releases/qt/) | 5.x | No |  |  |
 | XCB |  |  |  |  | [Yes](https://github.com/bitcoin/bitcoin/blob/master/depends/packages/qt.mk#L87) (Linux only) |
 | xkbcommon |  |  |  |  | [Yes](https://github.com/bitcoin/bitcoin/blob/master/depends/packages/qt.mk#L86) (Linux only) |
-| ZeroMQ | [4.2.3](https://github.com/zeromq/libzmq/releases) |  | No |  |  |
+| ZeroMQ | [4.2.5](https://github.com/zeromq/libzmq/releases) | 4.0.0 | No |  |  |
 | zlib | [1.2.11](https://zlib.net/) |  |  |  | No |
diff --git a/doc/zmq.md b/doc/zmq.md
index 5d67df9d22..a1a506f2e7 100644
--- a/doc/zmq.md
+++ b/doc/zmq.md
@@ -33,8 +33,10 @@ buffering or reassembly.
 
 ## Prerequisites
 
-The ZeroMQ feature in Bitcoin Core requires ZeroMQ API version 4.x or
-newer. Typically, it is packaged by distributions as something like
+The ZeroMQ feature in Bitcoin Core requires the ZeroMQ API >= 4.0.0
+[libzmq](https://github.com/zeromq/libzmq/releases).
+For version information, see [dependencies.md](dependencies.md).
+Typically, it is packaged by distributions as something like
 *libzmq3-dev*. The C++ wrapper for ZeroMQ is *not* needed.
 
 In order to run the example Python client scripts in contrib/ one must