[SjLj] Replace recursive block marking algorithm with iterative algorithm

Summary:
Some programs run into a stack overflow issue. This change avoids this
problem by replacing the recursive algorithm with the iterative version.

Reviewers: MatzeB, t.p.northover, dblaikie

Reviewed By: MatzeB

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D35105

llvm-svn: 307860