Update CI with testing framework from eigen_ci_cross_testing.

ci/scripts/test.windows.after_script.ps1

@@ -0,0 +1,17 @@
+# Change to build directory.
+$rootdir = Get-Location
+cd ${EIGEN_CI_BUILDDIR}
+
+# Determine the appropriate test tag and results file.
+$TEST_TAG = Get-Content Testing\TAG | select -first 1
+
+# PowerShell equivalent to xsltproc:
+$XSL_FILE = Resolve-Path "..\ci\CTest2JUnit.xsl"
+$INPUT_FILE = Resolve-Path Testing\$TEST_TAG\Test.xml
+$OUTPUT_FILE = Join-Path -Path $pwd -ChildPath JUnitTestResults_$CI_JOB_ID.xml
+$xslt = New-Object System.Xml.Xsl.XslCompiledTransform;
+$xslt.Load($XSL_FILE)
+$xslt.Transform($INPUT_FILE,$OUTPUT_FILE)
+
+# Return to root directory.
+cd ${rootdir}