Related to PR19992: when the GNU alignof-expression extension is applied to an
expression of array-of-unknown-bound type, don't try to complete the array
bound, and return the alignment of the element type rather than 1.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@210608 91177308-0d34-0410-b5e6-96231b3b80d8