Otherwise, the generated Makefile is included in the NSIS-installed documentation, which can lead to non-determinism (eg, if gawk is installed on some build VMs, but others only have mawk)
Backport of core PR14018
https://github.com/bitcoin/bitcoin/pull/14018/files
I was hoping that it would make the gitian windows build deterministic
but it is not enough. Still good to backport anyway.