Enable `-Wunused-variable` in velox/PACKAGE #15345

Job	Run time
Build	49m 4s
Build with Clang	0s
Spark Aggregate Fuzzer	15m 45s
Join Fuzzer	17m 32s
Presto Bias Fuzzer	0s
Presto Fuzzer	30m 46s
Exchange Fuzzer	16m 27s
Biased Aggregation Fuzzer with Presto as source of truth	0s
Aggregation Fuzzer with Presto as source of truth	25m 44s
Window Fuzzer with Presto as source of truth	18m 21s
Biased Expression Fuzzer with Only Added/Updated Functions and Presto as source of truth	0s
Writer Fuzzer with Presto as source of truth	17m 36s
RowNumber Fuzzer	15m 39s
Spark Bias Fuzzer	0s
Spark Fuzzer	15m 47s
Signature Changes	2s
	3h 42m 43s

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