[stack protector] Set edge weights for newly created basic blocks.

This commit fixes a bug in stack protector pass where edge weights were not set
when new basic blocks were added to lists of successor basic blocks.

Differential Revision: http://reviews.llvm.org/D5766


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222987 91177308-0d34-0410-b5e6-96231b3b80d8