Function LLVMGetModuleFlag 

pub unsafe extern "C" fn LLVMGetModuleFlag(
    M: LLVMModuleRef,
    Key: *const c_char,
    KeyLen: usize,
) -> LLVMMetadataRef

Add a module-level flag to the module-level flags metadata if it doesn’t already exist.

@see Module::getModuleFlag()