(cherry-pick): Fix warning when building on Linux #507

Job	Run time
build (gcc)	1m 37s
test (gcc)	4m 0s
build (gcc, CFLAGS=-DTK_NO_DEPRECATED=1)	1m 42s
test (gcc, --disable-xft)	4m 14s
build (gcc, --disable-xft)	1m 40s
test (gcc, --enable-symbols)	3m 32s
build (gcc, --disable-xss)	1m 56s
build (gcc, --enable-symbols)	1m 14s
build (clang)	2m 15s
build (clang, CFLAGS=-DTK_NO_DEPRECATED=1)	2m 17s
build (clang, --disable-xft)	2m 30s
build (clang, --disable-xss)	2m 18s
build (clang, --enable-symbols)	1m 30s
	30m 45s

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