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/builtins/gen/var/trunc/562d05.wgsl.expected.fxc.hlsl

@@ -0,0 +1,31 @@
+void trunc_562d05() {
+  float3 arg_0 = (0.0f).xxx;
+  float3 res = trunc(arg_0);
+}
+
+struct tint_symbol {
+  float4 value : SV_Position;
+};
+
+float4 vertex_main_inner() {
+  trunc_562d05();
+  return (0.0f).xxxx;
+}
+
+tint_symbol vertex_main() {
+  const float4 inner_result = vertex_main_inner();
+  tint_symbol wrapper_result = (tint_symbol)0;
+  wrapper_result.value = inner_result;
+  return wrapper_result;
+}
+
+void fragment_main() {
+  trunc_562d05();
+  return;
+}
+
+[numthreads(1, 1, 1)]
+void compute_main() {
+  trunc_562d05();
+  return;
+}

test/tint/builtins/gen/var/trunc/e183aa.wgsl.expected.fxc.hlsl

@@ -0,0 +1,31 @@
+void trunc_e183aa() {
+  float4 arg_0 = (0.0f).xxxx;
+  float4 res = trunc(arg_0);
+}
+
+struct tint_symbol {
+  float4 value : SV_Position;
+};
+
+float4 vertex_main_inner() {
+  trunc_e183aa();
+  return (0.0f).xxxx;
+}
+
+tint_symbol vertex_main() {
+  const float4 inner_result = vertex_main_inner();
+  tint_symbol wrapper_result = (tint_symbol)0;
+  wrapper_result.value = inner_result;
+  return wrapper_result;
+}
+
+void fragment_main() {
+  trunc_e183aa();
+  return;
+}
+
+[numthreads(1, 1, 1)]
+void compute_main() {
+  trunc_e183aa();
+  return;
+}

test/tint/builtins/gen/var/trunc/eb83df.wgsl.expected.fxc.hlsl

@@ -0,0 +1,31 @@
+void trunc_eb83df() {
+  float arg_0 = 1.0f;
+  float res = trunc(arg_0);
+}
+
+struct tint_symbol {
+  float4 value : SV_Position;
+};
+
+float4 vertex_main_inner() {
+  trunc_eb83df();
+  return (0.0f).xxxx;
+}
+
+tint_symbol vertex_main() {
+  const float4 inner_result = vertex_main_inner();
+  tint_symbol wrapper_result = (tint_symbol)0;
+  wrapper_result.value = inner_result;
+  return wrapper_result;
+}
+
+void fragment_main() {
+  trunc_eb83df();
+  return;
+}
+
+[numthreads(1, 1, 1)]
+void compute_main() {
+  trunc_eb83df();
+  return;
+}

test/tint/builtins/gen/var/trunc/f370d3.wgsl.expected.fxc.hlsl

@@ -0,0 +1,31 @@
+void trunc_f370d3() {
+  float2 arg_0 = (0.0f).xx;
+  float2 res = trunc(arg_0);
+}
+
+struct tint_symbol {
+  float4 value : SV_Position;
+};
+
+float4 vertex_main_inner() {
+  trunc_f370d3();
+  return (0.0f).xxxx;
+}
+
+tint_symbol vertex_main() {
+  const float4 inner_result = vertex_main_inner();
+  tint_symbol wrapper_result = (tint_symbol)0;
+  wrapper_result.value = inner_result;
+  return wrapper_result;
+}
+
+void fragment_main() {
+  trunc_f370d3();
+  return;
+}
+
+[numthreads(1, 1, 1)]
+void compute_main() {
+  trunc_f370d3();
+  return;
+}