This is a hack, because make has no way to serialize processing
of a target (just .NOTPARALLEL for the whole Makefile).
It uses the lockfile tool / liblockfile 1.17. Since that polls
the file, I adjusted the poll timeout to 5s max, because I found
the 60s wait much too long. Guess even 1s would be ok...
Since it's just a small build tool, I simply copied and patched
its source, instead of creating an external project. And there
is --with-system-lockfile=... to use an external binary instead.
Change-Id: I16bc4579a273dcf1aac811ae4723ca325a0b9eba
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/126152
Tested-by: Jenkins
Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>