pbrt-v4 as an external lib fails to create pbrt_soa.h

I have a relatively simple CMAKE file to add pbrt-v4 as part of a project



```cmake

cmake_minimum_required(VERSION 3.12)



set(PROJECT_NAME "pbrt-cpp")

project(${PROJECT_NAME})

set(SOURCE_FILES main.cpp)



include_directories(

  external/pbrt-v4/src/pbrt

  ${CMAKE_BINARY_DIR}/external/pbrt-v4/src/pbrt

)



set(CMAKE_MODULE_PATH ${CMAKE_SOURCE_DIR}/external/pbrt-v4/cmake)



add_definitions(-D PBRT_FLOAT_AS_DOUBLE)

add_subdirectory(external/pbrt-v4)



add_executable(${PROJECT_NAME} ${SOURCE_FILES})

target_compile_features(${PROJECT_NAME} PRIVATE cxx_std_17)



target_link_libraries(${PROJECT_NAME}

  pbrt

  pbrt::pbrt_lib # Tried with both pbrt_lib and pbrt and with and without pbrt::

)

```



The configuring part goes nicely, but immediately run into an error when I try to build:

`[build] ninja: error: '../../../src/pbrt/pbrt.soa', needed by 'external/pbrt-v4/pbrt_soa.h', missing and no known rule to make it`



I appreciate any help that I can get

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