Fixed directory to which arith.h gets written

[cvanaret]

Hi,
I'm trying to cross-compile solvers2 on Yggdrasil and I realized that arith.h gets written to the wrong directory (${CMAKE_CURRENT_BINARY_DIR} instead of ${GENERATED_INCLUDE_DIR}).

How to reproduce the error:

# xtool.cmake
set(CMAKE_SYSTEM_NAME Linux)
set(CMAKE_SYSTEM_PROCESSOR x86_64)
set(CMAKE_C_COMPILER cc)
set(CMAKE_CXX_COMPILER c++)

then

cmake -S . -B build -DCMAKE_TOOLCHAIN_FILE=xtool.cmake -DBUILD_SHARED_LIBS=ON

We get the following error message:

  Cannot find source file:

    .../asl/build/include/arith.h