Copy (zlib1|libssp-0).dll to \src\test\ to run test-process.exe.

This patch ensures that AppVeyor copies over libssp-0.dll and zlib1.dll
to src/test/ to make sure we can run text-process.exe from our slow
tests.

See: https://bugs.torproject.org/28179

.appveyor.yml

@@ -73,6 +73,8 @@ test_script:
             $buildpath = @("C:\msys64\${env:compiler_path}\bin") + $oldpath
             $env:Path = $buildpath -join ';'
             Set-Location "${env:build}"
+            Copy-Item "C:/msys64/${env:compiler_path}/bin/libssp-0.dll" -Destination "${env:build}/src/test"
+            Copy-Item "C:/msys64/${env:compiler_path}/bin/zlib1.dll" -Destination "${env:build}/src/test"
             Execute-Bash "VERBOSE=1 make -j2 check"
     }