[FS#908] x86: Xen support broken in 17.01.2 and later

[LEDE Bugs]

The following task has a new comment added:

FS#908 - x86: Xen support broken in 17.01.2 and later
User who did this - Baptiste Jonglez (bjonglez)

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As expected, I bisected it back to af1d1ebdda59602cbb61c84a103a1149a054a1b4 (""x86: enable 4G high memory support for generic (32bit) subtarget)
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More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=908#comment2967