Add new lock-obj-pub for sparc64-unknown-linux-gnu.

* src/syscfg/lock-obj-pub.sparc64-unknown-linux-gnu.h: New.
* src/Makefile.am (lock_obj_pub): Add.

Helmut Grohne writes:

Julien Cristau pointed out that sparc porter machines run 64bit kernels
and can execute 64bit executables. So here we go. I crossed
gen-posix-lock-obj for sparc64, verified that it is indeed a 64bit
executable and attach its output.

• Debian-bug-id: #762322