Did you try using this toolchain for compiling?
https://github.com/koreader/koxtoolchain
As for Kindle devices using v5.x firmware branch stuff is usually compiled to target ABI and use certain compiler flags in groups like this:
1) Kindle Touch & PW1
2) PW2 and all later models, all the way to firmware 5.16.2.1.1 ( = the last "soft float" firmware)
3) armhf ABI / firmware 5.16.3 and later.
So then you have situation that all models released between PW4 and PW6 could be on armel or armhf ABI depending on if the device is on older or latest available firmware for that particular model. Thus the end user needs to know and use correct binaries.
Like, I have a PW5 on 5.16.2.1.1 firmware that I do not want to ever update to newer, armhf firmware.