The fullbuild mode of LLVM’s libc is the mode in which it is to be used as
the only libc (as opposed to the Overlay Mode in which it is used along
with the system libc.) In to order use it as the only libc, one will have to
build and install not only the static archives like
libc.a from LLVM’s libc,
but also the start-up objects like
crt1.o and the public headers.
The full libc build can be of two types: