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>

src/tint/val/hlsl.cc

@@ -95,13 +95,15 @@ Result HlslUsingDXC(const std::string& dxc_path,
 }
 
 #ifdef _WIN32
-Result HlslUsingFXC(const std::string& source, const EntryPointList& entry_points) {
+Result HlslUsingFXC(const std::string& fxc_path,
+                    const std::string& source,
+                    const EntryPointList& entry_points) {
     Result result;
 
     // This library leaks if an error happens in this function, but it is ok
     // because it is loaded at most once, and the executables using HlslUsingFXC
     // are short-lived.
-    HMODULE fxcLib = LoadLibraryA("d3dcompiler_47.dll");
+    HMODULE fxcLib = LoadLibraryA(fxc_path.c_str());
     if (fxcLib == nullptr) {
         result.output = "Couldn't load FXC";
         result.failed = true;

src/tint/val/val.h

@@ -30,6 +30,9 @@ namespace tint::val {
 
 using EntryPointList = std::vector<std::pair<std::string, ast::PipelineStage>>;
 
+/// Name of the FXC compiler DLL
+static constexpr const char kFxcDLLName[] = "d3dcompiler_47.dll";
+
 /// The return structure of Validate()
 struct Result {
     /// True if validation passed
@@ -51,10 +54,13 @@ Result HlslUsingDXC(const std::string& dxc_path,
 #ifdef _WIN32
 /// Hlsl attempts to compile the shader with FXC, verifying that the shader
 /// compiles successfully.
+/// @param fxc_path path to the FXC DLL
 /// @param source the generated HLSL source
 /// @param entry_points the list of entry points to validate
 /// @return the result of the compile
-Result HlslUsingFXC(const std::string& source, const EntryPointList& entry_points);
+Result HlslUsingFXC(const std::string& fxc_path,
+                    const std::string& source,
+                    const EntryPointList& entry_points);
 #endif  // _WIN32
 
 /// Msl attempts to compile the shader with the Metal Shader Compiler,