complete/fix support of ctors/dtors and tls.
    
    + do not build libc.so with -DSHARED for the midipix targets.
    + provide surrogate init/fini arrays that allow invocation of the
      ctors/dtors iteration routines.
    + provide a builtin tls for the first thread.
    + update __copy_tls to match the layout of the simplified struct __tls.
    
    signed-off by Z. Gilboa; see copying.midipix (9cd0746c) for additional information.