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/expressions/splat/call/bool.wgsl.expected.fxc.hlsl

@@ -0,0 +1,17 @@
+[numthreads(1, 1, 1)]
+void unused_entry_point() {
+  return;
+}
+
+bool get_bool() {
+  return true;
+}
+
+void f() {
+  const bool tint_symbol = get_bool();
+  bool2 v2 = bool2((tint_symbol).xx);
+  const bool tint_symbol_1 = get_bool();
+  bool3 v3 = bool3((tint_symbol_1).xxx);
+  const bool tint_symbol_2 = get_bool();
+  bool4 v4 = bool4((tint_symbol_2).xxxx);
+}

test/tint/expressions/splat/call/f32.wgsl.expected.fxc.hlsl

@@ -0,0 +1,17 @@
+[numthreads(1, 1, 1)]
+void unused_entry_point() {
+  return;
+}
+
+float get_f32() {
+  return 1.0f;
+}
+
+void f() {
+  const float tint_symbol = get_f32();
+  float2 v2 = float2((tint_symbol).xx);
+  const float tint_symbol_1 = get_f32();
+  float3 v3 = float3((tint_symbol_1).xxx);
+  const float tint_symbol_2 = get_f32();
+  float4 v4 = float4((tint_symbol_2).xxxx);
+}

test/tint/expressions/splat/call/i32.wgsl.expected.fxc.hlsl

@@ -0,0 +1,17 @@
+[numthreads(1, 1, 1)]
+void unused_entry_point() {
+  return;
+}
+
+int get_i32() {
+  return 1;
+}
+
+void f() {
+  const int tint_symbol = get_i32();
+  int2 v2 = int2((tint_symbol).xx);
+  const int tint_symbol_1 = get_i32();
+  int3 v3 = int3((tint_symbol_1).xxx);
+  const int tint_symbol_2 = get_i32();
+  int4 v4 = int4((tint_symbol_2).xxxx);
+}

test/tint/expressions/splat/call/u32.wgsl.expected.fxc.hlsl

@@ -0,0 +1,17 @@
+[numthreads(1, 1, 1)]
+void unused_entry_point() {
+  return;
+}
+
+uint get_u32() {
+  return 1u;
+}
+
+void f() {
+  const uint tint_symbol = get_u32();
+  uint2 v2 = uint2((tint_symbol).xx);
+  const uint tint_symbol_1 = get_u32();
+  uint3 v3 = uint3((tint_symbol_1).xxx);
+  const uint tint_symbol_2 = get_u32();
+  uint4 v4 = uint4((tint_symbol_2).xxxx);
+}