sparc64, vdso: sparc64 vDSO implementation.

sparc64, vdso: sparc64 vDSO implementation.

This commit adds a vDSO similar to that used on x86: in this commit, that vDSO
is empty bar the ELF note used by glibc to verify that it knows about this vDSO.
The vDSO's location is somewhat randomized, so, as a consequence, tends to
randomize the locations of other shared libraries too.  (The randomization
respects /proc/sys/kernel/randomize_va_space.)

It is derived from the implementation in recent kernels, in that it uses a C
generator to translate the vDSO shared library into C code and validate that it
contains no relocations and the like.

Notes for future improvement:

 - There is no support for a vDSO in 32-bit userspace yet.  This is just because
   I want to get the sparc64 version working first: the compat vDSO
   implementation adds significant complexity.

 - The vDSO randomization process is ugly: we are calling get_unmapped_area()
   twice, with a randomization in the middle.  Eventually,
   arch_get_unmapped_area() on SPARC64 should learn about PF_RANDOMIZE, as it
   has on other arches.

Orabug: 20861959
Signed-off-by: Nick Alcock <nick.alcock@oracle.com>
Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
(cherry picked from commit 2da875e6f5781dd196e9f055cd53a3ac0d80aaaa)