* Add support for uClinux's broken munmap, contingent on

* Add support for uClinux's broken munmap, contingent on
  __UCLIBC_UCLINUX_BROKEN_MUNMAP__ (which is currently not defined anywhere).
  This makes other cases a tiny bit less efficient too.
* Move the malloc lock into the heap structure (locking is still done
  at the malloc level though, not by the heap functions).
* Initialize the malloc heap to contain a tiny initial static free-area so
  that programs that only do a very little allocation won't ever call mmap.