When running tests with "make check" on a host with gcc >= 14,
tests/boot/init.c is failing to build with error:

    init.c:6:9: error: implicit declaration of function 'puts' [-Wimplicit-function-declaration]
        6 |         puts("hello, KVM guest!\r");

    init.c:8:9: error: implicit declaration of function 'reboot' [-Wimplicit-function-declaration]
        8 |         reboot(LINUX_REBOOT_CMD_RESTART);

This is due to gcc 14 starting to treat implicit function
declarations as error, by default. See [1].

This commit fixes the issue by including the appropriate headers
(<stdio.h> for puts() and <sys/reboot.h> for reboot()). While at
it, <unistd.h> is also removed since it is not needed.

[1] https://gcc.gnu.org/gcc-14/porting_to.html#implicit-function-declaration

Signed-off-by: Julien Olivain <ju.o@free.fr>
---
 tests/boot/init.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tests/boot/init.c b/tests/boot/init.c
index 094f8ba..ea0d57f 100644
--- a/tests/boot/init.c
+++ b/tests/boot/init.c
@@ -1,5 +1,6 @@
 #include <linux/reboot.h>
-#include <unistd.h>
+#include <sys/reboot.h>
+#include <stdio.h>
 
 int main(int argc, char *argv[])
 {
-- 
2.55.0