tests/timer_api: Make sure constant time conversions are constants

When the timer frequency is known at compile time, make sure we can use any
time conversion macro as a global initializer.

Signed-off-by: Keith Packard <[email protected]>

Author: keith-packard

tests/kernel/timer/timer_api/src/timer_convert.c

@@ -33,7 +33,16 @@ struct test_rec {
 			(void *)test_##src##_to_##dst##_##round##prec	\
 	}								\
 
+#ifdef CONFIG_TIMER_READS_ITS_FREQUENCY_AT_RUNTIME
+#define TESTVAR(src, dst, round, prec)
+#else
+#define TESTVAR(src, dst, round, prec)					\
+	uint##prec##_t test_##src##_to_##dst##_##round##prec##_val =	\
+		k_##src##_to_##dst##_##round##prec(42);
+#endif
+
 #define TESTFUNC(src, dst, round, prec)					\
+	TESTVAR(src, dst, round, prec)					\
 	static uint##prec##_t test_##src##_to_##dst##_##round##prec(uint##prec##_t t) { \
 		return k_##src##_to_##dst##_##round##prec(t);		\
 	}