based on mpyth findings, and for those that are like me:
- impatient to get it working back on raspberry pi 1 (and cannot wait for a -welcome- proper fix to come along)
- that cannot rely on their pacman cache to downgrade "cleanly/saferly" (damn tiny SDcard I use for Arch - that "force" me to clear that cache frequently - or maybe I should consider a hard link or something...)
- that are reckless (as in ready to install packages from untrusted third-party repositories occasionally)
- here is the only place I found a glibc-2.23.x package < 2.23.4 online for raspberry pi 1 (armv6h), after going through tens of (official or not) mirrors (couldn't find 2.23.2 or 2.23.3)
$this->bbcode_second_pass_code('', 'sudo pacman -U http://fraggod.net/static/mirror/packages/archlinuxarm/armv6h/glibc-2.23-1-armv6h.pkg.tar.xz')
this got btsync 2.3.7-1 working again for me on my pi 1.
btw, at this moment, if you are on armv7h or armv5, there are better workarounds than downgrading glibc (see AUR link in OP).