Now let's say you do have a license, and the license is GPL. The license says that you have permission as long you do not combine the library using a linker with other programs that is not GPL. Do you have permission to copy the work if you disregard the conditions of the license? Likely answer: no.
Copyright do have a few exceptions. If you bought a copyrighted work like say Microsoft Word, there is an exception that says that you can also make a copy in memory in order to run it. Copyright law in some countries needed to be updated to do this, while in other places it occurred through precedents, but it was something that needed to occur. There might also exist a similar exception for running the program under Microsoft Windows, including using libraries called DLLs. Exceptions to the exclusivity of copyright is sometimes needed in order for the world to make sense.
The legal question then that remain is if the situation with FictitiousLibC has such an exception. That is less certain. There might be a copyright law exception, or there might not exist. What do you think?