Merge commit 8e34dd941 from llvm git (by Sanjay Patel):

[x86] avoid crashing when splitting AVX stores with non-simple type
(PR43916)

The store splitting transform was assuming a simple type (MVT), but
that's not necessarily the case as shown in the test.

This should fix 'Assertion failed: (isSimple() && "Expected a
SimpleValueType!")' when building the security/openssl111 port targeting
a CPU that supports AVX, but not AVX2, such as sandybridge.

PR: 241747
MFC after: 1 month
X-MFC-With: r353358