scripted-diff: s/WITH_MULTIPROCESS/ENABLE_IPC/ in cmake

Rename WITH_MULTIPROCESS to ENABLE_IPC, because ENABLE_IPC is a more accurate
name for the feature. It controls whether the src/ipc/ directory is built and
whether IPC features like -ipcbind, -ipcconnect, and -ipcfd are available. It
does NOT currently enable multiprocess features which are implemented in #10102
building on top of the IPC features. It will also no longer (as of the next
commit), control whether a find_package call is made so the "WITH_" prefix is
also inappropriate.

-BEGIN VERIFY SCRIPT-
git grep -l WITH_MULTIPROCESS | xargs sed -i s/WITH_MULTIPROCESS/ENABLE_IPC/g
-END VERIFY SCRIPT-

depends/toolchain.cmake.in

@@ -159,9 +159,9 @@ else()
 endif()
 
 if("@multiprocess@" STREQUAL "1")
-  set(WITH_MULTIPROCESS ON CACHE BOOL "")
+  set(ENABLE_IPC ON CACHE BOOL "")
   set(Libmultiprocess_ROOT "${CMAKE_CURRENT_LIST_DIR}" CACHE PATH "")
   set(LibmultiprocessNative_ROOT "${CMAKE_CURRENT_LIST_DIR}/native" CACHE PATH "")
 else()
-  set(WITH_MULTIPROCESS OFF CACHE BOOL "")
+  set(ENABLE_IPC OFF CACHE BOOL "")
 endif()