Fix missing stdarg.h include in test_comprehensive.cu

Added #include <stdarg.h> for va_start, va_end, and va_list used in
the log_test() variadic function.

Author: nishitnshah

test_comprehensive.cu

@@ -35,6 +35,7 @@
 #include <time.h>
 #include <string.h>
 #include <stdint.h>
+#include <stdarg.h>
 #include <pthread.h>
 #include <errno.h>
 #include <atomic>