Fix compiler warnings in Zephyr and FlexPRET support files #3193

Job	Run time
check-labels / check	8s
build-trace-tools / run (ubuntu-latest)	2s
build-rti / docker-build	1m 7s
build-trace-tools / run (macos-latest)	7s
build-trace-tools / run (windows-latest)	34s
fetch-lf / extract-ref	2s
build-rti / native-build (ubuntu-latest)	7s
unit-tests-multi / run (ubuntu-latest)	9s
build-rti / native-build (macos-latest)	8s
unit-tests-multi / run (macos-latest)	11s
unit-tests-single / run (ubuntu-latest)	7s
build-rti / native-build (windows-latest)	11s
unit-tests-single / run (macos-latest)	18s
lf-default-flexpret / flexpret-tests	6m 11s
lf-default-arduino / arduino-tests (ubuntu-latest)	5m 13s
lf-adaptive / regular-tests (ubuntu-latest)	26m 10s
lf-default / regular-tests (ubuntu-latest)	26m 1s
lf-default-arduino / arduino-tests (macos-latest)	6m 11s
lf-adaptive / regular-tests (macos-latest)	28m 45s
lf-default / regular-tests (macos-latest)	25m 11s
lf-adaptive / regular-tests (windows-latest)	1h 31m 1s
lf-default-zephyr / zephyr-tests	12m 33s
lf-default / regular-tests (windows-latest)	1h 32m 27s
lf-gedf-np / regular-tests (ubuntu-latest)	25m 55s
lf-gedf-np / regular-tests (macos-latest)	25m 12s
lf-python / regular-tests (ubuntu-latest)	23m 42s
lf-gedf-np / regular-tests (windows-latest)	1h 29m 12s
lf-python / regular-tests (macos-latest)	21m 51s
lf-python / regular-tests (windows-latest)	1h 9m 9s
	9h 37m 55s

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