A recent commit moved some Haiku-specific code parts from oslib-posix.c
to cutils.c, but failed to move the corresponding header #include
statement, too, so "make vm-build-haiku.x86_64" is currently broken.
Fix it by moving the header #include, too.

Fixes: 06680b15 ("include: move qemu_*_exec_dir() to cutils")
Message-Id: <20220718172026.139004-1-thuth@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>