Examples: Exclude encoder wheel clock example from RP2350 builds.

Borrows a check against the hardware_rtc target from Pico Examples.

Author: Gadgetoid

examples/breakout_encoder_wheel/CMakeLists.txt

@@ -1,6 +1,10 @@
 add_subdirectory(buttons)
 add_subdirectory(chase_game)
+if (TARGET hardware_rtc)
 add_subdirectory(clock)
+else()
+    message("Skipping breakout_encoder_wheel/clock example as hardware_rtc is unavailable on this platform")
+endif()
 add_subdirectory(colour_picker)
 add_subdirectory(encoder)
 add_subdirectory(gpio_pwm)