Handle vlas during inline cost computation if they'll be turned
into a constant size alloca by inlining.

Ran a run over the testsuite, no results out of the noise, fixes
the testcase in the PR.

PR19115.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205710 91177308-0d34-0410-b5e6-96231b3b80d8
Revert the last couple of patches here and go back to something
that at least failed reliably.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205711 91177308-0d34-0410-b5e6-96231b3b80d8