Create tag-release.sh script to tag a release and update README.md.

The README.md needs updating so that the labels it refers to exist
in the GitHub Releases. The `tag-release.sh` script should do that.

crosscompile/tag-release.sh

@@ -0,0 +1,48 @@
+#!/bin/bash
+##
+# Tag and update a release's links.
+#
+# We will update the release files to contain the tag for the new
+# release, as it will appear. Primarily this means updating the
+# README.md to have links to where the release will appear once
+# release has been made.
+# Then commiting the change, and finally tagging it.
+#
+
+set -eo pipefail
+
+tagscriptdir="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd -P)"
+tagrootdir="$(cd "$tagscriptdir/.." && pwd -P)"
+
+sed_inline_args=(-E -i)
+if [[ "$(uname -s)" = 'Darwin' ]] ; then
+    # On macOS we need to specify the backup filename to sed.
+    sed_inline_args+=('')
+fi
+
+cd "$tagrootdir"
+
+eval $("${tagscriptdir}"/ci-vars --repo .)
+
+if [[ "$CI_BRANCH_VERSION" =~ /-dirty$/ ]] ; then
+    echo "Branch is dirty. Refusing to continue."
+    exit 1
+fi
+
+sed "${sed_inline_args[@]}" 's!(https://github.com/gerph/riscos-prminxml-tool/releases/download)/[^/]*/(POSIX-PRMinXML|RISCOS-PRMinXML|Example-Output)-.*(\.zip|\.tar\.gz)!\1/GITTAG/\2-GITTAG\3!g' "README.md"
+git commit -m "Update README.md links for release" README.md
+
+
+eval $("${tagscriptdir}"/ci-vars --repo .)
+
+TAG="v$CI_BRANCH_VERSION"
+echo "New tag will be: $TAG"
+
+sed "${sed_inline_args[@]}" "s!GITTAG!$TAG!g" README.md
+git commit -m "Update README.md links for release $TAG" --amend README.md
+git tag -f "$TAG"
+
+echo "---- Update complete ----"
+echo "Now you must push the changes:"
+echo "    git push origin $CI_BRANCH"
+echo "    git push origin $TAG"