Update CI with testing framework from eigen_ci_cross_testing.

ci/scripts/test.windows.script.ps1

@@ -0,0 +1,30 @@
+# Change to build directory.
+$rootdir = Get-Location
+cd $EIGEN_CI_BUILDDIR
+
+# Determine number of processors for parallel tests.
+$NPROC=${Env:NUMBER_OF_PROCESSORS}
+
+# Set target based on regex or label.
+$target = ""
+if (${EIGEN_CI_TEST_REGEX}) {
+  $target = "-R","${EIGEN_CI_TEST_REGEX}"
+} elseif (${EIGEN_CI_TEST_LABEL}) {
+  $target = "-L","${EIGEN_CI_TEST_LABEL}"
+}
+
+# Repeat tests up to three times to ignore flakes.  Do not re-run with -T test,
+# otherwise we lose test results for those that passed.
+# Note: starting with CMake 3.17, we can use --repeat until-pass:3, but we have
+#       no way of easily installing this on ppc64le.
+ctest -j$NPROC --output-on-failure --no-compress-output --build-no-clean -T test $target || `
+  ctest -j$NPROC --output-on-failure --no-compress-output --rerun-failed || `
+  ctest -j$NPROC --output-on-failure --no-compress-output --rerun-failed
+
+$success = $LASTEXITCODE
+
+# Return to root directory.
+cd ${rootdir}
+
+# Explicitly propagate exit code to indicate pass/failure of test command.
+if($success -ne 0) { Exit $success }