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.