cmake: Add libnatpmp optional package support

cmake/module/FindNATPMP.cmake

@@ -0,0 +1,32 @@
+# Copyright (c) 2023-present The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or https://opensource.org/license/mit/.
+
+find_path(NATPMP_INCLUDE_DIR
+  NAMES natpmp.h
+)
+
+find_library(NATPMP_LIBRARY
+  NAMES natpmp
+)
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(NATPMP
+  REQUIRED_VARS NATPMP_LIBRARY NATPMP_INCLUDE_DIR
+)
+
+if(NATPMP_FOUND AND NOT TARGET NATPMP::NATPMP)
+  add_library(NATPMP::NATPMP UNKNOWN IMPORTED)
+  set_target_properties(NATPMP::NATPMP PROPERTIES
+    IMPORTED_LOCATION "${NATPMP_LIBRARY}"
+    INTERFACE_INCLUDE_DIRECTORIES "${NATPMP_INCLUDE_DIR}"
+  )
+  set_property(TARGET NATPMP::NATPMP PROPERTY
+    INTERFACE_COMPILE_DEFINITIONS USE_NATPMP=1 $<$<PLATFORM_ID:Windows>:NATPMP_STATICLIB>
+  )
+endif()
+
+mark_as_advanced(
+  NATPMP_INCLUDE_DIR
+  NATPMP_LIBRARY
+)