"I am about to give up."

You didn't tell us much about your setup (which perl related packages you have, see the tutorial I linked to), some searches show build logs on openwrt which include extern.h. Maybe talk to the openwrt people, explain your setup and your problem? Failing that cross compile what you want for your target system.

In reply to Re^6: EXTERN.h missing when compiling on OpenWrt by marto
in thread EXTERN.h missing when compiling on OpenWrt by morgon

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