A libc in LLVM

I think I might share similar concerns with Zachary, however mine is more of a confusion.

How would this work to have two libc’s at the same time? If my program is linked against this libc, but I am using a library linked to the system libc, how does shared state work/ If I setlocale(3) in my program, it wont affect the library which is using a different libc like would be expected, correct?