lvgl_sys build tries to compile unrelated C code

[sasq64]

It seems that the build process just tries to build any discovered C files in the project directory ?
or instance, here it finds our json library and fails to compile it;

 DEP_LV_CONFIG_PATH=`pwd` cargo build
   Compiling lvgl-sys v0.6.2
The following warnings were emitted during compilation:

warning: lvgl-sys@0.6.2: /Users/sasq/elux/wm-application/external/lwjson/test/test.c:2:10: fatal error: 'lwjson/lwjson.h' file not found
warning: lvgl-sys@0.6.2: #include "lwjson/lwjson.h"
warning: lvgl-sys@0.6.2:          ^~~~~~~~~~~~~~~~~
warning: lvgl-sys@0.6.2: 1 error generated.

error: failed to run custom build command for `lvgl-sys v0.6.2`