Fix build with old kernel headers

* strace.c (print_debug_info, maybe_allocate_tcb, print_signalled,
print_exited): Remove "const" qualifier from status variable to
workaround some old implementations of WIFSIGNALED/WIFSTOPPED/WIFEXITED
macros.
* v4l2.c: Include <linux/types.h>.
(v4l2_ioctl): Check that V4L2_CTRL_FLAG_NEXT_CTRL and VIDIOC_S_EXT_CTRLS
macros are defined.
* tests/Makefile.am (AM_CPPFLAGS): Define.
diff --git a/strace.c b/strace.c
index f851c98..0e131a1 100644
--- a/strace.c
+++ b/strace.c
@@ -2030,7 +2030,7 @@
 }
 
 static void
-print_debug_info(const int pid, const int status)
+print_debug_info(const int pid, int status)
 {
 	const unsigned int event = (unsigned int) status >> 16;
 	char buf[sizeof("WIFEXITED,exitcode=%u") + sizeof(int)*3 /*paranoia:*/ + 16];
@@ -2077,7 +2077,7 @@
 }
 
 static struct tcb *
-maybe_allocate_tcb(const int pid, const int status)
+maybe_allocate_tcb(const int pid, int status)
 {
 	if (!WIFSTOPPED(status)) {
 		if (detach_on_execve && pid == strace_child) {
@@ -2160,7 +2160,7 @@
 }
 
 static void
-print_signalled(struct tcb *tcp, const int pid, const int status)
+print_signalled(struct tcb *tcp, const int pid, int status)
 {
 	if (pid == strace_child) {
 		exit_code = 0x100 | WTERMSIG(status);
@@ -2184,7 +2184,7 @@
 }
 
 static void
-print_exited(struct tcb *tcp, const int pid, const int status)
+print_exited(struct tcb *tcp, const int pid, int status)
 {
 	if (pid == strace_child) {
 		exit_code = WEXITSTATUS(status);