Add missing required-features for examples

Previously, a build with `--examples` just failed for some combinations
of features. This should unsure that builds no longer fail in confusing
ways.

Author: hannobraun

Cargo.toml

@@ -80,14 +80,30 @@ debug = true
 lto = true
 
 
+[[example]]
+name = "irq_button"
+required-features = ["rt"]
+
 [[example]]
 name = "qspi"
 required-features = ["rt", "stm32l4x5"]
 
+[[example]]
+name = "rng"
+required-features = ["unproven"]
+
+[[example]]
+name = "rtc_alarm"
+required-features = ["rt"]
+
 [[example]]
 name = "rtic_frame_serial_dma"
 required-features = ["rt", "stm32l4x2"]
 
+[[example]]
+name = "timer"
+required-features = ["rt"]
+
 [[example]]
 name = "usb_serial"
 required-features = ["rt", "stm32l4x2", "stm32-usbd"]