Fix PR25339: ARM Constant Island

Summary:
Currently, the ARM Constant Island may not converge (or not converge quickly).
This patch let it move to the closest water after the user if it doesn't converge after 15 iterations.

This address https://llvm.org/bugs/show_bug.cgi?id=25339

Reviewers: t.p.northover, srhines, kristof.beyls, aadg, rengolin

Subscribers: weimingz, aemerson, rengolin, llvm-commits

Differential Revision: http://reviews.llvm.org/D16890

llvm-svn: 261665