sparc start.S does not provide the final argument for
__libc_start_main, which is the highest stack address used to
update the __libc_stack_end.A
This fixes elf/tst-execstack-prog-static-tunable on sparc64.
On sparcv9 this does not happen because the kernel puts an
auxv value, which turns to point to a value in the stack itself.
Checked on sparc64-linux-gnu.
Reviewed-by: Florian Weimer <fweimer@redhat.com>