Don't pass outdated -D__undef_<feature> flags to clang (#606)

The flags were removed in
llvm/llvm-project@423bdb2b

Author: wenju-he

options_compile.cpp

@@ -330,21 +330,6 @@ std::string EffectiveOptionsFilter::processOptions(const OpenCLArgList &args,
 		    parsedOclCFeatures.insert(a);
                 });
 
-  // "opencl-c-base.h" unconditionally enables a list of so-called "optional
-  // core" language features. We need to undef those that aren't explicitly
-  // defined within the compilation command (which would suggest that the
-  // target platform supports the corresponding feature).
-  const char* optionalCoreOclCFeaturesList[] = {
-      "__opencl_c_work_group_collective_functions",
-      "__opencl_c_atomic_order_seq_cst",
-      "__opencl_c_atomic_scope_device",
-      "__opencl_c_atomic_scope_all_devices",
-      "__opencl_c_read_write_images" };
-  for (std::string OclCFeature : optionalCoreOclCFeaturesList) {
-    if (!parsedOclCFeatures.contains(std::string("-D") + OclCFeature))
-      effectiveArgs.push_back(std::string("-D__undef_") + OclCFeature);
-  }
-
   // extension is enabled in PCH but disabled or not specifed in options =>
   // disable pch
   bool useModules =