Function llvm_sys_featured::core::LLVMGetModuleFlag

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

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