[XCOFF][AIX] Put each jump table in an independent section if -ffunction-sections is specified

If a function is in a unique section, putting all jump tables in
 .rodata will prevent functions that have a jump table to get
garbage collect by the linker.
Therefore, we need to put jump table into a unique section as well.

Reviewed By: Xiangling_L

Differential Revision: https://reviews.llvm.org/D84761