Roll SPIRV-Tools from 502e98295625 to 6fac705e7616 (7 revisions)

https://chromium.googlesource.com/external/github.com/KhronosGroup/SPIRV-Tools.git/+log/502e98295625..6fac705e7616

2020-10-19 afdx@google.com spirv-val: Fix validation of OpPhi instructions (#3919)
2020-10-19 afdx@google.com spirv-fuzz: Avoid void struct member when outlining functions (#3936)
2020-10-19 afdx@google.com spirv-fuzz: Do not allow Block-decorated structs when adding parameters (#3931)
2020-10-19 afdx@google.com spirv-fuzz: Fix to operand id type (#3937)
2020-10-19 afdx@google.com spirv-fuzz: Handle dead blocks in TransformationEquationInstruction (#3933)
2020-10-19 afdx@google.com spirv-fuzz: Do not allow sampled image load when flattening conditionals (#3930)
2020-10-19 afdx@google.com spirv-fuzz: Take care of OpPhi instructions when inlining (#3939)

If this roll has caused a breakage, revert this CL and stop the roller
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https://autoroll.skia.org/r/spirv-tools-chromium-autoroll
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Change-Id: I4f3a6977cab44d24ece2e4e364eaa7227f1dfce3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2486859Reviewed-by: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Commit-Queue: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#818838}

DEPS

@@ -313,7 +313,7 @@ vars = {
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling feed
   # and whatever else without interference from each other.
-  'spv_tools_revision': '502e98295625f5f07c7373d959e3403be5aa9de7',
+  'spv_tools_revision': '6fac705e76165663544e8562537c4165d3bac190',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling feed
   # and whatever else without interference from each other.