You can list all flags that you need in cmake toolchain file and pass to ExternalProject_Add
only one option: CMAKE_TOOLCHAIN_FILE
.
> cat CMakeLists.txt
cmake_minimum_required(VERSION 2.8)
project(Foo)
message("SOME_ARG1: ${SOME_ARG1}")
message("SOME_ARG2: ${SOME_ARG2}")
> cat MyToolchain.cmake
set(SOME_ARG1 "arg1")
set(SOME_ARG2 "arg2")
> cmake -H. -B_builds/notoolchain
...
-- Detecting CXX compiler ABI info - done
SOME_ARG1:
SOME_ARG2:
-- Configuring done
> cmake -H. -B_builds/toolchain -DCMAKE_TOOLCHAIN_FILE=MyToolchain.cmake
...
-- Detecting CXX compiler ABI info - done
SOME_ARG1: arg1
SOME_ARG2: arg2
-- Configuring done