Clang: disable the llvm.dbg.declare -> value instcombine for realz

It turns out the first attempt (#502428) got the flag backwards.
*headdesks*

Bug: 761633,765793,775258
Change-Id: I6ef2203822c4b0a5d04d6c8d564e0d347b2d104d
Reviewed-on: https://chromium-review.googlesource.com/724263Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Hans Wennborg <hans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#509640}

build/config/compiler/BUILD.gn

@@ -430,7 +430,7 @@ config("compiler") {
       "-Xclang",
       "-mllvm",
       "-Xclang",
-      "-instcombine-lower-dbg-declare=1",
+      "-instcombine-lower-dbg-declare=0",
     ]
   }