fix PR5436 by making the 'simple' case of SRoA not promote out of range

array indexes.  The "complex" case of SRoA still handles them, and correctly.

This fixes a weirdness where we'd correctly avoid transforming A[0][42] if
the 42 was too large, but we'd only do it if it was one gep, not two separate
ones.

llvm-svn: 90007