Merging r281479:

------------------------------------------------------------------------
r281479 | nemanja.i.ibm | 2016-09-14 07:19:09 -0700 (Wed, 14 Sep 2016) | 9 lines

Fix code-gen crash on Power9 for insert_vector_elt with variable index (PR30189)

This patch corresponds to review:
https://reviews.llvm.org/D24021

In the initial implementation of this instruction, I forgot to account for
variable indices. This patch fixes PR30189 and should probably be merged into
3.9.1 (I'll open a bug according to the new instructions).

------------------------------------------------------------------------

llvm-svn: 287809