Instantiate a stubbed SPIR-V parser if file ends in .spv

- spv parser just errors out for now
- link against SPIRV-Tools-opt
- Fixe CMake variable TINT_ENABLE_SPV_PARSER --> TINT_BUILD_SPV_PARSER

Bug: tint:3
Change-Id: Ie4ef9b03e001fca3cc11f65a425612755857feac
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/16600
Reviewed-by: dan sinclair <dsinclair@google.com>

src/CMakeLists.txt

@@ -305,8 +305,9 @@ add_library(libtint ${TINT_LIB_SRCS})
 tint_default_compile_options(libtint)
 set_target_properties(libtint PROPERTIES OUTPUT_NAME "tint")
 
-if(${TINT_ENABLE_SPV_PARSER})
-  target_link_libraries(libtint SPIRV-Tools)
+if(${TINT_BUILD_SPV_PARSER})
+  # We'll use the optimizer for its nice SPIR-V in-memory representation
+  target_link_libraries(libtint SPIRV-Tools-opt SPIRV-Tools)
 endif()
 
 add_executable(tint_unittests ${TINT_TEST_SRCS})

src/reader/spv/parser.cc

@@ -25,6 +25,7 @@ Parser::Parser(const std::vector<uint32_t>&) : Reader() {}
 Parser::~Parser() = default;
 
 bool Parser::Parse() {
+  set_error("SPIR-V parsing is not supported yet");
   return false;
 }
 

src/reader/spv/parser.h

@@ -31,6 +31,7 @@ class Parser : public Reader {
   /// Creates a new parser
   /// @param input the input data to parse
   explicit Parser(const std::vector<uint32_t>& input);
+  /// Destructor
   ~Parser() override;
 
   /// Run the parser