Good to see it works, and thanks for the set of steps.
In the interests of TIMTOWTDI, steps 4-7 could be simplified using cpanm. Calling cpanm --look opens a shell in the build directory. On Windows it is a cmd chell.
(Untested)
cpanm --look Compress::Stream::Zstd
:: You are now in the build dir
:: This next line prints the location of the Alien::Zstd files, under
+which will be libzstd.a
perl -MAlien::Zstd -E"say Alien::Zstd->dist_dir"
:: assuming it is in the dir you noted in your post the line would be
copy c:/Strawberry/perl/site/lib/auto/share/dist/Alien-zstd/lib/libzst
+d.a ext\zstd\lib
:: (One could also use File::Copy to use perl to find and copy the fil
+e in one step)
:: build, test, install
perl .\Build.PL && build && build test && build install
:: back to your previous shell
exit
