Squashed commit of the following:
Correct some additional compile-related issues.
Move include/nuttx/binfmt/builtin.h to include/nuttx/lib/builtin.h. Move apps/builtin/lib_builtin_forindex.c to libs/libc/builtin/lib_builtin_forindex.c.
Move binfmt/libbuiltin to libs/libc/builtin. There are calls made directly from apps/nshlib into this logic and hence, must be part of a library that can be shared between the OS and applications.
