wasm: implement error_set_has_value

This implements the safety check for error casts. The instruction
generates a jump table with 2 possibilities. The operand is used
as an index into the jump table. For cases where the value does
not exist within the error set, it will generate a jump to the
'false' block. For cases where it does exist, it will generate
a jump to the 'true' block. By calculating the highest and lowest
value we can keep the jump table smaller, as it doesn't need to
contain an index into the entire error set.

src/Module.zig

@@ -6626,7 +6626,7 @@ pub fn backendSupportsFeature(mod: Module, feature: Feature) bool {
         .safety_check_formatted => mod.comp.bin_file.options.use_llvm,
         .error_return_trace => mod.comp.bin_file.options.use_llvm,
         .is_named_enum_value => mod.comp.bin_file.options.use_llvm,
-        .error_set_has_value => mod.comp.bin_file.options.use_llvm,
+        .error_set_has_value => mod.comp.bin_file.options.use_llvm or mod.comp.bin_file.options.target.isWasm(),
         .field_reordering => mod.comp.bin_file.options.use_llvm,
     };
 }