Use flexible array members for structs that end with var-sized arrays

- Since Clang++, G++, and VC++ all support this extension (even though it's
  technically officially only part of C99), use it. It lets Clang's array-
  bounds checker know that these are meant to be accessed out of their so-called
  "bounds".

src/r_plane.cpp

@@ -558,8 +558,8 @@ static visplane_t *new_visplane (unsigned hash)
 
 	if (check == NULL)
 	{
-		check = (visplane_t *)M_Malloc (sizeof(*check) + sizeof(*check->top)*(MAXWIDTH*2));
-		memset(check, 0, sizeof(*check) + sizeof(*check->top)*(MAXWIDTH*2));
+		check = (visplane_t *)M_Malloc (sizeof(*check) + 3 + sizeof(*check->top)*(MAXWIDTH*2));
+		memset(check, 0, sizeof(*check) + 3 + sizeof(*check->top)*(MAXWIDTH*2));
 		check->bottom = check->top + MAXWIDTH+2;
 	}
 	else if (NULL == (freetail = freetail->next))

src/r_plane.h

@@ -63,7 +63,7 @@ struct visplane_s
 
 	unsigned short *bottom;			// [RH] bottom and top arrays are dynamically
 	unsigned short pad;				//		allocated immediately after the
-	unsigned short top[3];			//		visplane.
+	unsigned short top[];			//		visplane.
 };
 typedef struct visplane_s visplane_t;
 

src/stringtable.cpp

@@ -55,7 +55,7 @@ struct FStringTable::StringEntry
 	StringEntry *Next;
 	char *Name;
 	BYTE PassNum;
-	char String[2];
+	char String[];
 };
 
 FStringTable::FStringTable ()
@@ -283,7 +283,7 @@ void FStringTable::LoadLanguage (int lumpnum, DWORD code, bool exactMatch, int p
 			}
 			if (entry == NULL || cmpval > 0)
 			{
-				entry = (StringEntry *)M_Malloc (sizeof(*entry) + strText.Len() + strName.Len());
+				entry = (StringEntry *)M_Malloc (sizeof(*entry) + strText.Len() + strName.Len() + 2);
 				entry->Next = *pentry;
 				*pentry = entry;
 				strcpy (entry->String, strText.GetChars());
@@ -409,7 +409,7 @@ void FStringTable::SetString (const char *name, const char *newString)
 	size_t namelen = strlen (name);
 
 	// Create a new string entry
-	StringEntry *entry = (StringEntry *)M_Malloc (sizeof(*entry) + newlen + namelen);
+	StringEntry *entry = (StringEntry *)M_Malloc (sizeof(*entry) + newlen + namelen + 2);
 	strcpy (entry->String, newString);
 	strcpy (entry->Name = entry->String + newlen + 1, name);
 	entry->PassNum = 0;

src/textures/textures.h

@@ -119,7 +119,7 @@ struct patch_t
 	SWORD			height; 
 	SWORD			leftoffset; 	// pixels to the left of origin 
 	SWORD			topoffset;		// pixels below the origin 
-	DWORD 			columnofs[8];	// only [width] used
+	DWORD 			columnofs[];	// only [width] used
 	// the [0] is &columnofs[width] 
 };