fix PR8769, a miscompilation by inliner when inlining a function with a byval

fix PR8769, a miscompilation by inliner when inlining a function with a byval
argument.  The generated alloca has to have at least the alignment of the
byval, if not, the client may be making assumptions that the new alloca won't
satisfy.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122234 91177308-0d34-0410-b5e6-96231b3b80d8