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so that the caller can use some name other than gcpro1.
(GCPRO1, UNGCPRO): Reimplement in terms of the new macros.
(Fx_create_frame, x_create_tip_frame, Fx_show_tip):
(Fx_backspace_delete_keys_p): Rename locals to avoid shadowing.
Some of these renamings use the new GCPRO1_VAR and UNGCPRO_VAR
macros.