tint/test-runner: Split expectations for FXC and DXC

Change tint's `--fxc` flag to take the path of the FXC compiler DLL.
Have tint attempt to validate with both FXC and DXC if `--validate` is
passed.

Fix the 'dirsWithNoPassExpectations' logic which looks like it got
broken with the tint -> dawn merge. It also incorrectly applied
filepath.FromSlash() on windows.

Change-Id: I0f46aa5c21bc48a2abc48402c41f846aff4a8633
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/96800
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Commit-Queue: Ben Clayton <bclayton@chromium.org>

test/tint/buffer/storage/static_index/read.wgsl.expected.fxc.hlsl

@@ -0,0 +1,44 @@
+struct Inner {
+  int x;
+};
+
+ByteAddressBuffer s : register(t0, space0);
+
+float2x3 tint_symbol_6(ByteAddressBuffer buffer, uint offset) {
+  return float2x3(asfloat(buffer.Load3((offset + 0u))), asfloat(buffer.Load3((offset + 16u))));
+}
+
+float3x2 tint_symbol_7(ByteAddressBuffer buffer, uint offset) {
+  return float3x2(asfloat(buffer.Load2((offset + 0u))), asfloat(buffer.Load2((offset + 8u))), asfloat(buffer.Load2((offset + 16u))));
+}
+
+Inner tint_symbol_9(ByteAddressBuffer buffer, uint offset) {
+  const Inner tint_symbol_11 = {asint(buffer.Load((offset + 0u)))};
+  return tint_symbol_11;
+}
+
+typedef Inner tint_symbol_10_ret[4];
+tint_symbol_10_ret tint_symbol_10(ByteAddressBuffer buffer, uint offset) {
+  Inner arr[4] = (Inner[4])0;
+  {
+    [loop] for(uint i_1 = 0u; (i_1 < 4u); i_1 = (i_1 + 1u)) {
+      arr[i_1] = tint_symbol_9(buffer, (offset + (i_1 * 4u)));
+    }
+  }
+  return arr;
+}
+
+[numthreads(1, 1, 1)]
+void main() {
+  const int3 a = asint(s.Load3(0u));
+  const int b = asint(s.Load(12u));
+  const uint3 c = s.Load3(16u);
+  const uint d = s.Load(28u);
+  const float3 e = asfloat(s.Load3(32u));
+  const float f = asfloat(s.Load(44u));
+  const float2x3 g = tint_symbol_6(s, 48u);
+  const float3x2 h = tint_symbol_7(s, 80u);
+  const Inner i = tint_symbol_9(s, 104u);
+  const Inner j[4] = tint_symbol_10(s, 108u);
+  return;
+}

test/tint/buffer/storage/static_index/write.wgsl.expected.fxc.hlsl

@@ -0,0 +1,46 @@
+struct Inner {
+  int x;
+};
+
+RWByteAddressBuffer s : register(u0, space0);
+
+void tint_symbol_6(RWByteAddressBuffer buffer, uint offset, float2x3 value) {
+  buffer.Store3((offset + 0u), asuint(value[0u]));
+  buffer.Store3((offset + 16u), asuint(value[1u]));
+}
+
+void tint_symbol_7(RWByteAddressBuffer buffer, uint offset, float3x2 value) {
+  buffer.Store2((offset + 0u), asuint(value[0u]));
+  buffer.Store2((offset + 8u), asuint(value[1u]));
+  buffer.Store2((offset + 16u), asuint(value[2u]));
+}
+
+void tint_symbol_9(RWByteAddressBuffer buffer, uint offset, Inner value) {
+  buffer.Store((offset + 0u), asuint(value.x));
+}
+
+void tint_symbol_10(RWByteAddressBuffer buffer, uint offset, Inner value[4]) {
+  Inner array[4] = value;
+  {
+    [loop] for(uint i_1 = 0u; (i_1 < 4u); i_1 = (i_1 + 1u)) {
+      tint_symbol_9(buffer, (offset + (i_1 * 4u)), array[i_1]);
+    }
+  }
+}
+
+[numthreads(1, 1, 1)]
+void main() {
+  s.Store3(0u, asuint((0).xxx));
+  s.Store(12u, asuint(0));
+  s.Store3(16u, asuint((0u).xxx));
+  s.Store(28u, asuint(0u));
+  s.Store3(32u, asuint((0.0f).xxx));
+  s.Store(44u, asuint(0.0f));
+  tint_symbol_6(s, 48u, float2x3((0.0f).xxx, (0.0f).xxx));
+  tint_symbol_7(s, 80u, float3x2((0.0f).xx, (0.0f).xx, (0.0f).xx));
+  const Inner tint_symbol_11 = (Inner)0;
+  tint_symbol_9(s, 104u, tint_symbol_11);
+  const Inner tint_symbol_12[4] = (Inner[4])0;
+  tint_symbol_10(s, 108u, tint_symbol_12);
+  return;
+}