Cannot override a CMake variable via catkin_make

edit

I'm trying to override a CMake variable defined in a CMakeLists.txt

set(ANTLR4_ROOT /usr/local)

via a, say,

catkin_make -DANTLR4_ROOT=$HOME/.local

. But it the value isn't changed.

I do know that the value is set because

message(STATUS "Using ANTLR4 version ${ANTLR4_VERSION}: ${ANTLR4_ROOT}")

always prints

-- Using ANTLR4 version 4.7.1: /usr/local

I am however able to alter, say,

catkin_make -DCMAKE_PREFIX_PATH=/xx

so then why can't I alter ANTLR4_ROOT in a similar way?