message: add check in amalgamation that makes sure we included the *amalgamation* duckdb.hpp
diff: @@ -147,6 +147,8 @@ def generate_amalgamation(source_file, header_file):
  with open(temp_source, 'w+') as sfile:
  header_file_name = header_file.split(os.sep)[-1]
  sfile.write('#include "' + header_file_name + '"\n\n')
  + sfile.write("#ifndef DUCKDB_AMALGAMATION\n#error header mismatch\n#endif\n\n")
  +
  for compile_dir in compile_directories:
  write_dir(compile_dir, sfile)
  # for windows we write file_system.cpp last
  