Add a Khronos-private version of known-good for SPIR-V Tools.

known_good_khr.json

+{
+  "commits" : [
+    {
+      "name" : "spirv-tools",
+      "site" : "gitlab",
+      "subrepo" : "spirv/spirv-tools",
+      "subdir" : "External/spirv-tools",
+      "commit" : "063dbea0f19a3926b81a34fa8dc5479fa7969739"
+    },
+    {
+      "name" : "spirv-tools/external/spirv-headers",
+      "site" : "gitlab",
+      "subrepo" : "spirv/SPIRV-Headers",
+      "subdir" : "External/spirv-tools/external/spirv-headers",
+      "commit" : "77240d9e86c6ff135f6de8c7b89a0099a2d90e16"
+    }
+  ]
+}