LLVM is recommending to use SmallVector (that is, omitting the N), in the absence of a well-motivated choice for the number of inlined elements N.
However, this doesn't work well with XL compiler on AIX since some header(s) aren't properly picked up with it. We need to take a further look into the real issue underneath and fix it in a later patch.
But currently we'd like to use this patch to unblock the build compiler issue first.
The first build failure was spot here: http://lab.llvm.org:8014/#/builders/126/builds/71