Update spirv-opt known-good

Notably, this includes the following:

- Fix exponential performance of DeadInsertElim
- Constant folding of OpVectorTimesScalar
- Add Vector DCE
- Add store-store elimination to LocalSingleBlockElim
- Improve folding of OpVectorTimesScalar and OpPhi
- Fixes handling of kill and unreachable ops in inlining

known_good.json

@@ -5,7 +5,7 @@
       "site" : "github",
       "subrepo" : "KhronosGroup/SPIRV-Tools",
       "subdir" : "External/spirv-tools",
-      "commit" : "c20a718e00876a91c868858e367b8f150a8d595a"
+      "commit" : "a00a0a09ae5dab8ef15073ceb40542c162767798"
     },
     {
       "name" : "spirv-tools/external/spirv-headers",