to determine which Elf Types are to be handled. Change the M4
templates to wrap an `#if __FreeBSD_version >= NNN'/`#endif' pair
around the generated code for each ELF data type, where `NNN' is
the OS version where the ELF type was added to the source tree.
This change allows cross-builds of old sources on newer FreeBSD
systems to work correctly.
Problem reported by: ru
