hack: make flexible union members work on gcc≤14

In GCC <= 14, flexible arrays are not supported in unions because of a parserlimitation.

This is a hack that declares an anonymous struct, which itself can contain a flexible array but still be a member of a union. Another empty element is included because structs that only contain a flexible array are also invalid.

database/database.h.in

@@ -735,10 +735,10 @@ typedef struct
     int		prop_len;	/* String length or number of values */
     union {
         Plane *prop_plane;	/* For PROPERTY_TYPE_PLANE */
-        int   prop_integer[];	/* For PROPERTY_TYPE_INTEGER or _DIMENSION */
-        dlong prop_double[];	/* For PROPERTY_TYPE_DOUBLE */
-        char  prop_string[];	/* For PROPERTY_TYPE_STRING, must be last in
-                                 * struct and union */
+        FLEX_UNION_MEMBER(int prop_integer[], 0);	/* For PROPERTY_TYPE_INTEGER or _DIMENSION */
+        FLEX_UNION_MEMBER(dlong prop_double[], 1);	/* For PROPERTY_TYPE_DOUBLE */
+        FLEX_UNION_MEMBER(char  prop_string[], 2);	/* For PROPERTY_TYPE_STRING, must be last in
+                                * struct and union */
     } prop_value;
 } PropertyRecord;
 

utils/hash.h

@@ -34,10 +34,10 @@ typedef struct h1
     char *h_pointer;		/* Pointer to anything. */
     struct h1 *h_next;		/* Next element, zero for end. */
     union {
-	const char *h_ptr;	/* One-word key value to identify entry. */
-    /* Following members must be the last part of the struct and union:*/
-	unsigned h_words[];	/* N-word key value. */
-	char h_name[];		/* Text name of this entry. */
+        const char *h_ptr;	/* One-word key value to identify entry. */
+        /* Following members must be the last part of the struct and union:*/
+        FLEX_UNION_MEMBER(unsigned h_words[], 0);	/* N-word key value. */
+        FLEX_UNION_MEMBER(char h_name[], 1);		/* Text name of this entry. */
     } h_key;
 } HashEntry;
 

utils/magic.h

@@ -286,6 +286,19 @@ extern char AbortMessage[];
   #endif
 #endif
 
+
+/*
+ * In GCC <= 14, flexible arrays are not supported in unions because of a parser
+ * limitation.
+ * 
+ * This is a hack that declares an anonymous struct, which itself can contain
+ * a flexible array but still be a member of a union. Another empty element is
+ * included because structs that only contain a flexible array are also invalid.
+ */
+#define FLEX_UNION_MEMBER(member, member_no) struct {\
+    char __empty ## member_no [0]; member;\
+}
+
 /* ------------------ End of Machine Configuration Section ----------------- */
 
 #endif /* _MAGIC__UTILS__MAGIC_H */