Patch soci only once:

* Patch the soci unsigned-types.h file. If no changes are made, delete
  the patched file and exit. If there are changes, backup the original
  and replace it with the patched file.
* Fixes XRPLF#3885

Builds/CMake/soci_patch.cmake

@@ -1,13 +1,30 @@
 # This patches unsigned-types.h in the soci official sources
 # so as to remove type range check exceptions that cause
 # us trouble when using boost::optional to select int values
+
+# Some versions of CMake erroneously patch external projects on every build.
+# If the patch makes no changes, skip it. This workaround can be
+# removed once we stop supporting vulnerable versions of CMake.
+# https://gitlab.kitware.com/cmake/cmake/-/issues/21086
 file (STRINGS include/soci/unsigned-types.h sourcecode)
+# Delete the .patched file if it exists, so it doesn't end up duplicated.
+# Trying to remove a file that does not exist is not a problem.
+file (REMOVE include/soci/unsigned-types.h.patched)
 foreach (line_ ${sourcecode})
   if (line_ MATCHES "^[ \\t]+throw[ ]+soci_error[ ]*\\([ ]*\"Value outside of allowed.+$")
     set (line_ "//${CMAKE_MATCH_0}")
   endif ()
   file (APPEND include/soci/unsigned-types.h.patched "${line_}\n")
 endforeach ()
+execute_process( COMMAND ${CMAKE_COMMAND} -E compare_files
+                 include/soci/unsigned-types.h include/soci/unsigned-types.h.patched
+                 RESULT_VARIABLE compare_result
+)
+if( compare_result EQUAL 0)
+  message(DEBUG "The soci source and patch files are identical. Make no changes.")
+  file (REMOVE include/soci/unsigned-types.h.patched)
+  return()
+endif()
 file (RENAME include/soci/unsigned-types.h include/soci/unsigned-types.h.orig)
 file (RENAME include/soci/unsigned-types.h.patched include/soci/unsigned-types.h)
 # also fix Boost.cmake so that it just returns when we override the Boost_FOUND var