man/: EXAMPLES: Add missing includes

Link: <https://github.com/include-what-you-use/include-what-you-use/pull/1283>
Link: <https://github.com/include-what-you-use/include-what-you-use/pull/1344>
Reported-by: iwyu(1) (`make lint-c-iwyu`)
Signed-off-by: Alejandro Colomar <alx@kernel.org>
24 files changed