Mark lua setjmp/longjmp for powerpc weak

Linux already defines setjmp/longjmp for powerpc, which leads to
duplicate symbols in a statically linked build.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Sterlng Jensen <sterlingjensen@users.noreply.github.com>
Closes #10795