FreeBSD port (36): config support

[Bruno Haible]

Roland McGrath writes:
> If you are using /usr/libexec/ld-elf.so.1 as the program interpreter name
> then it seems ill-advised to use a soname that is likely to one day
> conflict with the native FreeBSD libc's soname.

I'm using /usr/lib/ld.so.1 as program interpreter. But since only the programs
refer to it, not the shared libraries, ldconfig uses the referenced libc
version to infer whether each library is linked with FreeBSD libc or glibc.
I'm using the soname libc.so.1 now.

Bruno