device.h: conditionally remove init braces for C++20 compatibility

Conditionally remove braces for designated initializers of anonymous
unions. This makes it compatible with C++20 while not breaking pre-C11
gcc.

This does for device.h what commit c15f029 ("init.h: restore
designated initializers in SYS_INIT_NAMED()") did for init.h

See https://docs.zephyrproject.org/latest/develop/languages/cpp/ and
long discussion in zephyrproject-rtos#69411 for more obscure C/C++ compatibility details.

Signed-off-by: Marc Herbert <[email protected]>

include/zephyr/device.h

@@ -1080,11 +1080,22 @@ device_get_dt_nodelabels(const struct device *dev)
 			(.pm_constraints = (constraints_),))				\
 		IF_ENABLED(CONFIG_PM_POLICY_DEVICE_CONSTRAINTS,				\
 			(.pm_constraints_size = (constraints_size_),))			\
-		IF_ENABLED(CONFIG_PM_DEVICE, ({ .pm_base = (pm_),})) /**/		\
+		IF_ENABLED(CONFIG_PM_DEVICE, Z_DEVICE_INIT_PM_BASE(pm_)) /**/		\
 		IF_ENABLED(CONFIG_DEVICE_DT_METADATA,					\
 			   (.dt_meta = &Z_DEVICE_DT_METADATA_NAME_GET(dev_id_),))	\
 	}
 
+/*
+ * Anonymous unions require C11. Some pre-C11 gcc versions have early support for anonymous
+ * unions but they require these braces when combined with C99 designated initializers. For
+ * more details see https://docs.zephyrproject.org/latest/develop/languages/cpp/
+ */
+#if defined(__STDC_VERSION__) && (__STDC_VERSION__) < 201100
+#  define Z_DEVICE_INIT_PM_BASE(pm_) ({ .pm_base = (pm_),})
+#else
+#  define Z_DEVICE_INIT_PM_BASE(pm_)   (.pm_base = (pm_),)
+#endif
+
 /**
  * @brief Device section name (used for sorting purposes).
  *
@@ -1157,10 +1168,7 @@ device_get_dt_nodelabels(const struct device *dev)
 		Z_INIT_ENTRY_NAME(DEVICE_NAME_GET(dev_id)) = {                                     \
 			.init_fn = {COND_CODE_1(Z_DEVICE_IS_MUTABLE(node_id), (.dev_rw), (.dev)) = \
 					    (init_fn_)},                                           \
-			{                                                                          \
-				COND_CODE_1(Z_DEVICE_IS_MUTABLE(node_id), (.dev_rw), (.dev)) =     \
-					&DEVICE_NAME_GET(dev_id),                                  \
-			},                                                                         \
+			Z_DEVICE_INIT_ENTRY_DEV(node_id, dev_id),                                  \
 	}
 
 #define Z_DEFER_DEVICE_INIT_ENTRY_DEFINE(node_id, dev_id, init_fn_)                                \
@@ -1169,12 +1177,23 @@ device_get_dt_nodelabels(const struct device *dev)
 		Z_INIT_ENTRY_NAME(DEVICE_NAME_GET(dev_id)) = {                                     \
 			.init_fn = {COND_CODE_1(Z_DEVICE_IS_MUTABLE(node_id), (.dev_rw), (.dev)) = \
 					    (init_fn_)},                                           \
-			{                                                                          \
-				COND_CODE_1(Z_DEVICE_IS_MUTABLE(node_id), (.dev_rw), (.dev)) =     \
-					&DEVICE_NAME_GET(dev_id),                                  \
-			},                                                                         \
+			Z_DEVICE_INIT_ENTRY_DEV(node_id, dev_id),                                  \
 	}
 
+/*
+ * Anonymous unions require C11. Some pre-C11 gcc versions have early support for anonymous
+ * unions but they require these braces when combined with C99 designated initializers. For
+ * more details see https://docs.zephyrproject.org/latest/develop/languages/cpp/
+ */
+#if defined(__STDC_VERSION__) && (__STDC_VERSION__) < 201100
+#  define Z_DEVICE_INIT_ENTRY_DEV(node_id, dev_id) { Z_DEV_ENTRY_DEV(node_id, dev_id) }
+#else
+#  define Z_DEVICE_INIT_ENTRY_DEV(node_id, dev_id)   Z_DEV_ENTRY_DEV(node_id, dev_id)
+#endif
+
+#define Z_DEV_ENTRY_DEV(node_id, dev_id)                                                           \
+	COND_CODE_1(Z_DEVICE_IS_MUTABLE(node_id), (.dev_rw), (.dev)) =  &DEVICE_NAME_GET(dev_id)
+
 /**
  * @brief Define a @ref device and all other required objects.
  *