[PATCH v3] cyclictest: Fix BUILD failure for GCC_VER < 15

[Suneeth D <Suneeth.D@amd.com>]

timerthread() uses bool, true, and false. Those are keywords in C23,
which became GCC's default in GCC 15 (-std=gnu23), so the file compiles
there without stdbool.h. With GCC 14 and earlier the default is gnu17,
where they are provided by <stdbool.h>, and the build fails without it.

Fixes: 98fcd661ac59 (cyclictest: Acquire a lock before invoking pthread_cond_signal())
Closes: https://lore.kernel.org/linux-rt-users/4ce24139-5f7e-4180-a290-bcc15fb4f559@amd.com/
Signed-off-by: Suneeth D <Suneeth.D@amd.com>
Signed-off-by: John Kacur <jkacur@redhat.com>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---

Please ignore the previously sent v2. Sorry for the noise.

Changes since v2 ---> v3:

 * Add Signed-off tag by John Kacur

Changes since v1 ---> v2:

 * Modify commit message to include Tomas Glozar's note on default
   changes happened since GCC 15.

based on: fd45df830803dd7f26d2ca8bdcf05fd7e0d62ae8 (rt-tests/main)

 src/cyclictest/cyclictest.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/cyclictest/cyclictest.c b/src/cyclictest/cyclictest.c
index 99194378f946..58b56bcede0f 100644
--- a/src/cyclictest/cyclictest.c
+++ b/src/cyclictest/cyclictest.c
@@ -15,6 +15,7 @@
 #include <stdlib.h>
 #include <stdint.h>
 #include <stdarg.h>
+#include <stdbool.h>
 #include <unistd.h>
 #include <fcntl.h>
 #include <getopt.h>
-- 
2.43.0