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/loops/continue_in_switch.wgsl.expected.fxc.hlsl

@@ -0,0 +1,24 @@
+[numthreads(1, 1, 1)]
+void f() {
+  {
+    [loop] for(int i = 0; (i < 4); i = (i + 1)) {
+      bool tint_continue = false;
+      switch(i) {
+        case 0: {
+          {
+            tint_continue = true;
+            break;
+          }
+          break;
+        }
+        default: {
+          break;
+        }
+      }
+      if (tint_continue) {
+        continue;
+      }
+    }
+  }
+  return;
+}

test/tint/loops/loop.wgsl.expected.fxc.hlsl

@@ -0,0 +1,14 @@
+[numthreads(1, 1, 1)]
+void unused_entry_point() {
+  return;
+}
+
+int f() {
+  int i = 0;
+  [loop] while (true) {
+    i = (i + 1);
+    if ((i > 4)) {
+      return i;
+    }
+  }
+}

test/tint/loops/loop_with_continuing.wgsl.expected.fxc.hlsl

@@ -0,0 +1,16 @@
+[numthreads(1, 1, 1)]
+void unused_entry_point() {
+  return;
+}
+
+int f() {
+  int i = 0;
+  [loop] while (true) {
+    if ((i > 4)) {
+      return i;
+    }
+    {
+      i = (i + 1);
+    }
+  }
+}

test/tint/loops/nested_loops.wgsl.expected.fxc.hlsl

@@ -0,0 +1,21 @@
+[numthreads(1, 1, 1)]
+void unused_entry_point() {
+  return;
+}
+
+int f() {
+  int i = 0;
+  int j = 0;
+  [loop] while (true) {
+    i = (i + 1);
+    if ((i > 4)) {
+      return 1;
+    }
+    [loop] while (true) {
+      j = (j + 1);
+      if ((j > 4)) {
+        return 2;
+      }
+    }
+  }
+}

test/tint/loops/nested_loops_with_continuing.wgsl.expected.fxc.hlsl

@@ -0,0 +1,25 @@
+[numthreads(1, 1, 1)]
+void unused_entry_point() {
+  return;
+}
+
+int f() {
+  int i = 0;
+  int j = 0;
+  [loop] while (true) {
+    if ((i > 4)) {
+      return 1;
+    }
+    [loop] while (true) {
+      if ((j > 4)) {
+        return 2;
+      }
+      {
+        j = (j + 1);
+      }
+    }
+    {
+      i = (i + 1);
+    }
+  }
+}

test/tint/loops/while.wgsl.expected.fxc.hlsl

@@ -0,0 +1,12 @@
+[numthreads(1, 1, 1)]
+void unused_entry_point() {
+  return;
+}
+
+int f() {
+  int i = 0;
+  [loop] while((i < 4)) {
+    i = (i + 1);
+  }
+  return i;
+}

test/tint/loops/while_with_continue.wgsl.expected.fxc.hlsl

@@ -0,0 +1,13 @@
+[numthreads(1, 1, 1)]
+void unused_entry_point() {
+  return;
+}
+
+int f() {
+  int i = 0;
+  [loop] while((i < 4)) {
+    i = (i + 1);
+    continue;
+  }
+  return i;
+}