I am very happy to announce that git-annex v.7.20190129-3+b1 for armel works perfectly on my QNAP TS-219P (armv5tel)!
I ran the extensive test suite within git-annex, with "git-annex test" and all the 227 tests passed without error - here is the last line of that execution:
Please find attached entire (compressed) log of >2k lines, captured with "nohup git-annex test 2>&1 > git-annex-test.output &".
And here follows the transcript of the installation of git-annex from sid, confirming that it's the version you generated:
drakestail:/tmp/test# apt install -t sid git-annex
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following additional packages will be installed:
aria2 git git-man git-remote-gcrypt libaria2-0 libcom-err2 libcomerr2 libcurl3-gnutls liberror-perl libgssapi-krb5-2 libk5crypto3 libkrb5-3 libkrb5support0 libpcre2-8-0 nocache
Suggested packages:
git-daemon-run | git-daemon-sysvinit git-doc git-el git-email git-gui gitk gitweb git-cvs git-mediawiki git-svn xdot bup adb tor magic-wormhole tahoe-lafs uftp youtube-dl rclone krb5-doc krb5-user
The following NEW packages will be installed:
aria2 git git-annex git-man git-remote-gcrypt libaria2-0 libcom-err2 liberror-perl libpcre2-8-0 nocache
The following packages will be upgraded:
libcomerr2 libcurl3-gnutls libgssapi-krb5-2 libk5crypto3 libkrb5-3 libkrb5support0
6 upgraded, 10 newly installed, 0 to remove and 869 not upgraded.
Need to get 20.9 MB of archives.
After this operation, 111 MB of additional disk space will be used.
Do you want to continue? [Y/n]
Get:1
http://ftp.it.debian.org/debian sid/main armel libcom-err2 armel 1.45.2-1 [68.9 kB]
Get:2
http://ftp.it.debian.org/debian sid/main armel libcomerr2 armel 1.45.2-1 [65.5 kB]
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http://ftp.it.debian.org/debian buster/main armel libaria2-0 armel 1.34.0-4 [916 kB]
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http://ftp.it.debian.org/debian buster/main armel aria2 armel 1.34.0-4 [362 kB]
Get:5
http://ftp.it.debian.org/debian buster/main armel libgssapi-krb5-2 armel 1.17-3 [136 kB]
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http://ftp.it.debian.org/debian buster/main armel libkrb5-3 armel 1.17-3 [319 kB]
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http://ftp.it.debian.org/debian buster/main armel libk5crypto3 armel 1.17-3 [118 kB]
Get:8
http://ftp.it.debian.org/debian buster/main armel libkrb5support0 armel 1.17-3 [62.2 kB]
Get:9
http://ftp.it.debian.org/debian buster/main armel libcurl3-gnutls armel 7.64.0-4 [292 kB]
Get:10
http://ftp.it.debian.org/debian buster/main armel libpcre2-8-0 armel 10.32-5 [185 kB]
Get:11
http://ftp.it.debian.org/debian buster/main armel liberror-perl all 0.17027-2 [30.9 kB]
Get:12
http://ftp.it.debian.org/debian buster/main armel git-man all 1:2.20.1-2 [1,619 kB]
Get:13
http://ftp.it.debian.org/debian buster/main armel git armel 1:2.20.1-2 [4,402 kB]
Get:14
http://ftp.it.debian.org/debian sid/main armel git-annex armel 7.20190129-3+b1 [12.3 MB]
Get:15
http://ftp.it.debian.org/debian buster/main armel git-remote-gcrypt all 1.2-1 [15.8 kB]
Get:16
http://ftp.it.debian.org/debian buster/main armel nocache armel 1.1-1 [17.7 kB]
Fetched 20.9 MB in 3s (5,498 kB/s)
Reading changelogs... Done
(Reading database ... 100879 files and directories currently installed.)
Preparing to unpack .../libcomerr2_1.45.2-1_armel.deb ...
Unpacking libcomerr2:armel (1.45.2-1) over (1.43.4-2) ...
Selecting previously unselected package libcom-err2:armel.
Preparing to unpack .../libcom-err2_1.45.2-1_armel.deb ...
Unpacking libcom-err2:armel (1.45.2-1) ...
Setting up libcom-err2:armel (1.45.2-1) ...
Selecting previously unselected package libaria2-0:armel.
(Reading database ... 100882 files and directories currently installed.)
Preparing to unpack .../00-libaria2-0_1.34.0-4_armel.deb ...
Unpacking libaria2-0:armel (1.34.0-4) ...
Selecting previously unselected package aria2.
Preparing to unpack .../01-aria2_1.34.0-4_armel.deb ...
Unpacking aria2 (1.34.0-4) ...
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Unpacking libgssapi-krb5-2:armel (1.17-3) over (1.15-1+deb9u1) ...
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Unpacking libcurl3-gnutls:armel (7.64.0-4) over (7.52.1-5+deb9u9) ...
Selecting previously unselected package libpcre2-8-0:armel.
Preparing to unpack .../07-libpcre2-8-0_10.32-5_armel.deb ...
Unpacking libpcre2-8-0:armel (10.32-5) ...
Selecting previously unselected package liberror-perl.
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Unpacking liberror-perl (0.17027-2) ...
Selecting previously unselected package git-man.
Preparing to unpack .../09-git-man_1%3a2.20.1-2_all.deb ...
Unpacking git-man (1:2.20.1-2) ...
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Preparing to unpack .../10-git_1%3a2.20.1-2_armel.deb ...
Unpacking git (1:2.20.1-2) ...
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Unpacking git-annex (7.20190129-3+b1) ...
Selecting previously unselected package git-remote-gcrypt.
Preparing to unpack .../12-git-remote-gcrypt_1.2-1_all.deb ...
Unpacking git-remote-gcrypt (1.2-1) ...
Selecting previously unselected package nocache.
Preparing to unpack .../13-nocache_1.1-1_armel.deb ...
Unpacking nocache (1.1-1) ...
Setting up git-man (1:2.20.1-2) ...
Processing triggers for mime-support (3.60) ...
Setting up liberror-perl (0.17027-2) ...
Setting up nocache (1.1-1) ...
Setting up libkrb5support0:armel (1.17-3) ...
Processing triggers for libc-bin (2.28-10) ...
Processing triggers for man-db (2.7.6.1-2) ...
Setting up libcomerr2:armel (1.45.2-1) ...
Setting up libpcre2-8-0:armel (10.32-5) ...
Processing triggers for hicolor-icon-theme (0.15-1) ...
Setting up libaria2-0:armel (1.34.0-4) ...
Setting up libk5crypto3:armel (1.17-3) ...
Setting up aria2 (1.34.0-4) ...
Setting up libkrb5-3:armel (1.17-3) ...
Setting up libgssapi-krb5-2:armel (1.17-3) ...
Setting up libcurl3-gnutls:armel (7.64.0-4) ...
Setting up git (1:2.20.1-2) ...
Setting up git-annex (7.20190129-3+b1) ...
Setting up git-remote-gcrypt (1.2-1) ...
Processing triggers for libc-bin (2.28-10) ...
Thanks again to you and Paul for the work done.