[DebugInfo] Don't turn dbg.declare into DBG_VALUE for static allocas

Summary:
We already have information about static alloca stack locations in our
side table. Emitting instructions for them is inefficient, and it only
happens when the address of the alloca has been materialized within the
current block, which isn't often.

Reviewers: aprantl, probinson, dblaikie

Subscribers: jfb, dschuff, sbc100, jgravelle-google, hiraditya, llvm-commits, aheejin

Differential Revision: https://reviews.llvm.org/D36117

llvm-svn: 309729