[mlir][emitc] Don't convert unsupported types in EmitC

This PR adds check for unsupported types in emitc, which fixes a
crash.

Author: CoTinker

mlir/lib/Conversion/SCFToEmitC/SCFToEmitC.cpp

@@ -322,7 +322,11 @@ void SCFToEmitCPass::runOnOperation() {
   // Fallback converter
   // See note https://mlir.llvm.org/docs/DialectConversion/#type-converter
   // Type converters are called most to least recently inserted
-  typeConverter.addConversion([](Type t) { return t; });
+  typeConverter.addConversion([](Type type) -> std::optional<Type> {
+    if (emitc::isSupportedEmitCType(type))
+      return type;
+    return {};
+  });
   populateEmitCSizeTTypeConversions(typeConverter);
   populateSCFToEmitCConversionPatterns(patterns, typeConverter);