adapt code to new pattern since llvm#129689

Author: Keenuts

llvm/lib/Target/SPIRV/SPIRVCallLowering.cpp

@@ -280,6 +280,8 @@ getExecutionModel(const SPIRVSubtarget &STI, const Function &F) {
     const auto value = attribute.getValueAsString();
     if (value == "compute")
       return SPIRV::ExecutionModel::GLCompute;
+    if (value == "vertex")
+      return SPIRV::ExecutionModel::Vertex;
 
     report_fatal_error(
         "This HLSL entry point is not supported by this backend.");