vkernel - Bring back .hash section

vkernel - Bring back .hash section

  As of the switch to GCC 5 the default hash style to ld has changed from both
  (sysv,gnu) to gnu alone. This results in binaries without a .hash section
  which is fine for userland binaries but not for kernel ones since our kernel
  linker uses .hash section to resolve its own symbols.

  With the missing .hash section the vkernel kernel linker was not able do
  symbol lookups and that rendered kvm(3) useless and all its consumers stopped
  working.

  During the vkernel build, SYSTEM_LD is changed so that the normal buildkernel
  settings are overridden so by changing the parameters passed to ld we bring
  back the .hash section.