For a target with none of aligned_alloc, memalign etc. we defined our
own aligned_alloc using malloc, so we need a declaration of malloc. As
in libsupc++/new_op.cc we need to declare it ourselves for freestanding
environments.
libstdc++-v3/ChangeLog:
* libsupc++/new_opa.cc [!_GLIBCXX_HOSTED]: Declare malloc.
