Print an error when SPIR-V is requested and ENABLE_SPIRV=0 is set

This case fails slightly less silently now.
Also make ENABLE_OPT depend on ENABLE_SPIRV, since when there's no
SPIR-V optimization doesn't really make sense.

CMakeLists.txt

@@ -115,7 +115,7 @@ CMAKE_DEPENDENT_OPTION(ENABLE_EMSCRIPTEN_ENVIRONMENT_NODE
 option(ENABLE_HLSL "Enables HLSL input support" ON)
 option(ENABLE_RTTI "Enables RTTI")
 option(ENABLE_EXCEPTIONS "Enables Exceptions")
-option(ENABLE_OPT "Enables spirv-opt capability if present" ON)
+CMAKE_DEPENDENT_OPTION(ENABLE_OPT "Enables spirv-opt capability if present" ON "ENABLE_SPIRV" OFF)
 
 if(MINGW OR (APPLE AND ${CMAKE_CXX_COMPILER_ID} MATCHES "GNU"))
  # Workaround for CMake behavior on Mac OS with gcc, cmake generates -Xarch_* arguments

StandAlone/StandAlone.cpp

@@ -1507,9 +1507,9 @@ void CompileAndLinkShaderUnits(std::vector<ShaderCompUnit> compUnits)
 
  std::vector<std::string> outputFiles;
 
-#ifdef ENABLE_SPIRV
  // Dump SPIR-V
  if (Options & EOptionSpv) {
+#ifdef ENABLE_SPIRV
  CompileOrLinkFailed.fetch_or(CompileFailed);
  CompileOrLinkFailed.fetch_or(LinkFailed);
  if (static_cast<bool>(CompileOrLinkFailed.load()))
@@ -1569,8 +1569,10 @@ void CompileAndLinkShaderUnits(std::vector<ShaderCompUnit> compUnits)
  }
  }
  }
- }
+#else
+ Error("This configuration of glslang does not have SPIR-V support");
 #endif
+ }
 
  CompileOrLinkFailed.fetch_or(CompileFailed);
  CompileOrLinkFailed.fetch_or(LinkFailed);