Merge bitcoin/bitcoin#30903: cmake: Add FindZeroMQ module

915640e191 depends: zeromq: don't install .pc files and remove patches for them (Cory Fields)
6b8a74463b cmake: Add `FindZeroMQ` module (Hennadii Stepanov)

Pull request description:

  This PR introduces the `FindZeroMQ` module, which first attempts to find the `libzmq` library using CMake's `find_package()` and falls back to `pkg_check_modules()` if unsuccessful.

  Addresses https://github.com/bitcoin/bitcoin/issues/30876 for the ZeroMQ package.

ACKs for top commit:
  fanquake:
    ACK 915640e191

Tree-SHA512: 2f17bae21be5d3f280a13425d22f5d1b2e23837a8aaf5ec89c433767509de030a42d598b261e102bdb5b860d8ede98013c124c3d25e081e956d4ee3a81b2584f

cmake/module/FindZeroMQ.cmake

@@ -0,0 +1,41 @@
+# Copyright (c) 2024-present The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or https://opensource.org/license/mit/.
+
+#[=======================================================================[
+FindZeroMQ
+----------
+
+Finds the ZeroMQ headers and library.
+
+This is a wrapper around find_package()/pkg_check_modules() commands that:
+ - facilitates searching in various build environments
+ - prints a standard log message
+
+#]=======================================================================]
+
+include(FindPackageHandleStandardArgs)
+find_package(ZeroMQ ${ZeroMQ_FIND_VERSION} NO_MODULE QUIET)
+if(ZeroMQ_FOUND)
+  find_package_handle_standard_args(ZeroMQ
+    REQUIRED_VARS ZeroMQ_DIR
+    VERSION_VAR ZeroMQ_VERSION
+  )
+  if(TARGET libzmq)
+    add_library(zeromq ALIAS libzmq)
+  elseif(TARGET libzmq-static)
+    add_library(zeromq ALIAS libzmq-static)
+  endif()
+  mark_as_advanced(ZeroMQ_DIR)
+else()
+  find_package(PkgConfig REQUIRED)
+  pkg_check_modules(libzmq QUIET
+    IMPORTED_TARGET
+    libzmq>=${ZeroMQ_FIND_VERSION}
+  )
+  find_package_handle_standard_args(ZeroMQ
+    REQUIRED_VARS libzmq_LIBRARY_DIRS
+    VERSION_VAR libzmq_VERSION
+  )
+  add_library(zeromq ALIAS PkgConfig::libzmq)
+endif()