Fix PR6910.

Fix PR6910.

Limit alignment in SmallVector 8, otherwise GCC assumes 16 byte alignment.
opetaror new, and malloc only return 8-byte aligned memory on 32-bit Linux,
which cause a crash if code is compiled with -O3 (or -ftree-vectorize) and some
SmallVector code is vectorized.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@102604 91177308-0d34-0410-b5e6-96231b3b80d8