LoopVectorizer: Don't assert on the absence of induction variables

A computable loop exit count does not imply the presence of an induction
variable. Scalar evolution can return a value for an infinite loop.

Fixes PR15926.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181495 91177308-0d34-0410-b5e6-96231b3b80d8
Revert "Make sure debug info contains linkage names (DW_AT_MIPS_linkage_name)"
temporarily while investigating gdb.cp/templates.exp.

This reverts commit r181471.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181496 91177308-0d34-0410-b5e6-96231b3b80d8