Use FLEXIBLE_ARRAY_MEMBER in a bunch more places.

Replace some bogus "x[1]" declarations with "x[FLEXIBLE_ARRAY_MEMBER]".
Aside from being more self-documenting, this should help prevent bogus
warnings from static code analyzers and perhaps compiler misoptimizations.

This patch is just a down payment on eliminating the whole problem, but
it gets rid of a lot of easy-to-fix cases.

Note that the main problem with doing this is that one must no longer rely
on computing sizeof(the containing struct), since the result would be
compiler-dependent.  Instead use offsetof(struct, lastfield).  Autoconf
also warns against spelling that offsetof(struct, lastfield[0]).

Michael Paquier, review and additional fixes by me.

src/include/tsearch/dicts/regis.h

@@ -21,7 +21,7 @@ typedef struct RegisNode
 				len:16,
 				unused:14;
 	struct RegisNode *next;
-	unsigned char data[1];
+	unsigned char data[FLEXIBLE_ARRAY_MEMBER];
 } RegisNode;
 
 #define  RNHDRSZ	(offsetof(RegisNode,data))

src/include/tsearch/dicts/spell.h

@@ -49,7 +49,7 @@ typedef struct
 typedef struct SPNode
 {
 	uint32		length;
-	SPNodeData	data[1];
+	SPNodeData	data[FLEXIBLE_ARRAY_MEMBER];
 } SPNode;
 
 #define SPNHDRSZ	(offsetof(SPNode,data))
@@ -70,7 +70,7 @@ typedef struct spell_struct
 			int			len;
 		}			d;
 	}			p;
-	char		word[1];		/* variable length, null-terminated */
+	char		word[FLEXIBLE_ARRAY_MEMBER];
 } SPELL;
 
 #define SPELLHDRSZ	(offsetof(SPELL, word))
@@ -120,7 +120,7 @@ typedef struct AffixNode
 {
 	uint32		isvoid:1,
 				length:31;
-	AffixNodeData data[1];
+	AffixNodeData data[FLEXIBLE_ARRAY_MEMBER];
 } AffixNode;
 
 #define ANHRDSZ		   (offsetof(AffixNode, data))

src/include/tsearch/ts_type.h

@@ -63,7 +63,7 @@ typedef uint16 WordEntryPos;
 typedef struct
 {
 	uint16		npos;
-	WordEntryPos pos[1];		/* variable length */
+	WordEntryPos pos[FLEXIBLE_ARRAY_MEMBER];
 } WordEntryPosVector;
 
 
@@ -82,7 +82,7 @@ typedef struct
 {
 	int32		vl_len_;		/* varlena header (do not touch directly!) */
 	int32		size;
-	WordEntry	entries[1];		/* variable length */
+	WordEntry	entries[FLEXIBLE_ARRAY_MEMBER];
 	/* lexemes follow the entries[] array */
 } TSVectorData;
 
@@ -233,7 +233,7 @@ typedef struct
 {
 	int32		vl_len_;		/* varlena header (do not touch directly!) */
 	int32		size;			/* number of QueryItems */
-	char		data[1];		/* data starts here */
+	char		data[FLEXIBLE_ARRAY_MEMBER];	/* data starts here */
 } TSQueryData;
 
 typedef TSQueryData *TSQuery;