Extend commit 844d79916a (cmake --build: Add support for driving Xcode
workspaces, 2025-06-02) to support multiple `--target` arguments.
`xcodebuild -scheme` cannot be repeated in a single call, so call it
multiple times instead.
Issue: #26958
Co-Authored-By: Craig Scott <craig.scott@crascit.com>
External tools may create a `.xcworkspace` directory next to the
`.xcodeproj` directory that CMake generates. If a workspace exists,
drive the build through it instead.
Closes: #26958
Co-authored-by: Brad King <brad.king@kitware.com>