files:


external
├─ glad.c
├── include
│  ├── glad
│  │  └── glad.h
│  └── KHR
│     └── khrplatform.h



CMakeLists.txt:
include_directories(${CMAKE_CURRENT_SOURCE_DIR}/external/include)
file(GLOB BUTTERFLIES_SOURCES_C ${CMAKE_CURRENT_SOURCE_DIR} *.c external/glad.c)