Try using gcc asm with tcc in ed25519-donna-64

The tiny c compiler (TCC) claims to support GCC-style asm
statements.  If that's so, then this patch may successfully get it
to build ed25519-donna for X86_64.  If not, then at least this patch
should improve the error message that you get when your compiler
doesn't have a uint128_t, by telling you what to do to "fix" the
issue.

Closes #40240; bugfix on 0.2.9.4-alpha.
10 jobs for bug40240_045 in 30 minutes and 53 seconds (queued for 6 minutes and 21 seconds)
latest
Status Job ID Name Coverage
  Test
passed #14418
debian-disable-dirauth

00:06:01

passed #14419
debian-disable-relay

00:06:06

passed #14414
debian-distcheck

00:07:11

passed #14415
debian-docs

00:03:12

passed #14413
debian-hardened

00:07:52

passed #14556
debian-integration

00:15:10

passed #14412
debian-minimal

00:05:21

passed #14420
debian-nss

00:05:23

passed #14417
debian-tracing

00:07:51

failed #14416
debian-integration

00:14:35