find_program(CMAKE_C_COMPILER NAMES gcc cc)
if(NOT CMAKE_C_COMPILER)
    message(FATAL_ERROR "C compiler not found!")
endif()

set(OUTPUT_FILE ${CMAKE_BINARY_DIR}/libhello_c.so)

add_custom_command(
    OUTPUT ${OUTPUT_FILE}
    COMMAND ${CMAKE_C_COMPILER} -shared -fPIC -o ${OUTPUT_FILE} ${CMAKE_CURRENT_SOURCE_DIR}/hello.c
    DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/hello.c
    COMMENT "Compiling hello_c shared library..."
)

add_custom_target(hello_c ALL DEPENDS ${OUTPUT_FILE})