ed25519-donna doesn't build on arm without warnings with the stack protector
From Jenkins (https://jenkins.torproject.org/job/tor-ci-linux-master-extra-arm/147/ARCHITECTURE=armhf,SUITE=jessie/consoleFull):
13:54:27 ../tor/src/ext/ed25519/donna/ed25519_tor.c: In function 'curved25519_scalarmult_basepoint_donna':
13:54:27 ../tor/src/ext/ed25519/donna/ed25519_tor.c:107:12: error: stack protector not protecting local variables: variable length buffer [-Werror=stack-protector]
13:54:27 ED25519_FN(curved25519_scalarmult_basepoint) (curved25519_key pk, const curved25519_key e) {
13:54:27 ^
13:54:27 ../tor/src/ext/ed25519/donna/ed25519_tor.c:33:32: note: in definition of macro 'ED25519_FN3'
13:54:27 #define ED25519_FN3(fn,suffix) fn##suffix
Commit d8352646900c6316af8e2967742ce6a438b04221 should have fixed this, but apparently it's not enough. I'm just going to change the donna code to not align to 16 byte boundaries on ARM since that's only there for the SSE2 code in the first place.
On the off chance that the code does gain NEON support the penalty for unaligned access isn't that severe (there are load/store forms that require alignment, in which case the code will crash), but when that happens we can revisit this issue.