Update SPIRV-Tools known good.

Includes:

    Update OpPhi instructions after splitting block. (#1783)
    Don't change decorations and names in merge return. (#1777)
    Transform to combine consecutive access chains
    Handle undef literal value in vector shuffle
    Fix block ordering in dead branch elim
    Fix finding constant with particular type. (#1724)
    Fix infinite loop while folding OpVectorShuffle (#1722)
    Fix size error when folding vector shuffle. (#1721)
    Layout validation: Permit {vec3; float} tight packing

known_good.json

@@ -5,7 +5,7 @@
       "site" : "github",
       "subrepo" : "KhronosGroup/SPIRV-Tools",
       "subdir" : "External/spirv-tools",
-      "commit" : "9ecbcf5fc87db00d3d6275522c735b5667007647"
+      "commit" : "714bf84e58abd9573488fc365707fb8f288ca73c"
     },
     {
       "name" : "spirv-tools/external/spirv-headers",