CMake not only checks if the header exists, but tries to include and
compile it, which fails with linux/if.h since it needs another header
which it does not include itself.
Manually include it as a CFLAG in the CHECK_INCLUDE_FILE call to fix
it.
@ogasser noticed a small mistake in the previous PR - nothing bad as the include is only used to get a definition that is available as a fallback, but worth fixing anyway.
CMake not only checks if the header exists, but tries to include and compile it, which fails with linux/if.h since it needs another header which it does not include itself. Manually include it as a CFLAG in the CHECK_INCLUDE_FILE call to fix it.
@ogasser noticed a small mistake in the previous PR - nothing bad as the include is only used to get a definition that is available as a fallback, but worth fixing anyway.