Several vendors use EFI BC instead of the EFI x86-64 value for the arch, some thinkpads for example. We noticed this while we tried to use PXE on all our machines and that some EFI systems with 64-bit didn't work and some did. We then found the old commit that change the if clause from 00:07 to 00:09 and tested around. Thus we found out that some machines use 7 and some 9, so IMHO it's correct to redirect both cases to the 64bit syslinux filename. This commit doesn't break old configs, just adds the additional option.
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