Fix some compiler warnings, when compiling with g++ #3399

Job	Run time
build (gcc)	1m 51s
test (gcc)	4m 10s
build (gcc, CFLAGS=-DTK_NO_DEPRECATED=1)	1m 47s
test (gcc, --disable-xft)	4m 1s
build (gcc, --disable-shared)	1m 46s
test (gcc, --enable-symbols)	3m 25s
build (gcc, --disable-xft)	1m 44s
build (gcc, --disable-xss)	1m 38s
build (gcc, --enable-symbols)	1m 14s
build (clang)	1m 52s
build (clang, CFLAGS=-DTK_NO_DEPRECATED=1)	2m 32s
build (clang, --disable-shared)	2m 2s
build (clang, --disable-xft)	2m 0s
build (clang, --disable-xss)	1m 54s
build (clang, --enable-symbols)	1m 27s
	33m 23s

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