Update SPIRV-Tools submodule. (#5245)

This also required a fix to the unrolling loop, as the SPIRV optimizer
has changed upstream.

external/SPIRV-Tools

@@ -1 +1 @@
-Subproject commit e7c6084fd1d6d6f5ac393e842728d8be309688ca
+Subproject commit 23cb9b96cc2acf93e55839136b2c9643cbef6df6

tools/clang/test/CodeGenSPIRV/texture.sample-offset.with.loop-unroll.hlsl

@@ -3,7 +3,6 @@
 SamplerState      gSampler  : register(s5);
 Texture2D<float4> t         : register(t1);
 
-// CHECK: [[vi0:%\d+]] = OpConstantComposite %v2int %int_0 %int_0
 // CHECK: [[vi1:%\d+]] = OpConstantComposite %v2int %int_1 %int_1
 // CHECK: [[vi2:%\d+]] = OpConstantComposite %v2int %int_2 %int_2
 
@@ -12,7 +11,7 @@ float4 main(int2 offset: A) : SV_Target {
     float clamp = offset.x;
     float4 ret = 0;
 
-// CHECK: OpImageSampleExplicitLod %v4float {{%\d+}} {{%\d+}} Lod|ConstOffset %float_0 [[vi0]]
+// CHECK: OpImageSampleExplicitLod %v4float {{%\d+}} {{%\d+}} Lod %float_0
 // CHECK: OpImageSampleExplicitLod %v4float {{%\d+}} {{%\d+}} Lod|ConstOffset %float_0 [[vi1]]
 // CHECK: OpImageSampleExplicitLod %v4float {{%\d+}} {{%\d+}} Lod|ConstOffset %float_0 [[vi2]]