Bugfix: NSIS: Exclude Makefile* from docs
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
I was hoping that it would make the gitian windows build deterministic
but it is not enough. Still good to backport anyway.
Test Plan: Run the windows gitian builds.
Reviewers: #bitcoin_abc, deadalnix, jasonbcox
Reviewed By: #bitcoin_abc, jasonbcox
Differential Revision: https://reviews.bitcoinabc.org/D4015