Pick up SIZEOF_INT via ModelConstants

In backporting, sometimes the git history shows that something
has always had the same type, but the type was plain int rather
than an explicit-width type. So, for such things, there is no
need for a plethora of SIZEOF_FOO constants, but SIZEOF_INT may
be generally useful to detect if a platform has a surprising
value for that width.

pljava-so/src/main/c/ModelConstants.c

@@ -84,6 +84,7 @@ static int32 constants[] = {
 	CONSTANT(PG_VERSION_NUM),
 
 	CONSTANT(SIZEOF_DATUM),
+	CONSTANTEXPR(SIZEOF_INT, sizeof (int)),
 	CONSTANTEXPR(SIZEOF_SIZE, sizeof (Size)),
 
 	CONSTANT(ALIGNOF_SHORT),

pljava/src/main/java/org/postgresql/pljava/pg/ModelConstants.java

@@ -185,14 +185,15 @@ public void close()
 	@Native private static final int IDX_PG_VERSION_NUM          = 0;
 
 	@Native private static final int IDX_SIZEOF_DATUM            = 1;
-	@Native private static final int IDX_SIZEOF_SIZE             = 2;
+	@Native private static final int IDX_SIZEOF_INT              = 2;
+	@Native private static final int IDX_SIZEOF_SIZE             = 3;
 
-	@Native private static final int IDX_ALIGNOF_SHORT           = 3;
-	@Native private static final int IDX_ALIGNOF_INT             = 4;
-	@Native private static final int IDX_ALIGNOF_DOUBLE          = 5;
-	@Native private static final int IDX_MAXIMUM_ALIGNOF         = 6;
+	@Native private static final int IDX_ALIGNOF_SHORT           = 4;
+	@Native private static final int IDX_ALIGNOF_INT             = 5;
+	@Native private static final int IDX_ALIGNOF_DOUBLE          = 6;
+	@Native private static final int IDX_MAXIMUM_ALIGNOF         = 7;
 
-	@Native private static final int IDX_NAMEDATALEN             = 7;
+	@Native private static final int IDX_NAMEDATALEN             = 8;
 
 
 
@@ -298,6 +299,12 @@ public void close()
 	public static final int PG_VERSION_NUM;
 
 	public static final int SIZEOF_DATUM;
+	/*
+	 * In backporting, can be useful when the git history shows something was
+	 * always of 'int' type, so it doesn't need a dedicated SIZEOF_FOO, but does
+	 * need to notice if a platform has an unexpected 'int' width.
+	 */
+	public static final int SIZEOF_INT;
 	public static final int SIZEOF_SIZE;
 
 	public static final int ALIGNOF_SHORT;
@@ -413,6 +420,7 @@ public void close()
 			PG_VERSION_NUM    = n.get(IDX_PG_VERSION_NUM);
 
 			SIZEOF_DATUM      = n.get(IDX_SIZEOF_DATUM);
+			SIZEOF_INT        = n.get(IDX_SIZEOF_INT);
 			SIZEOF_SIZE       = n.get(IDX_SIZEOF_SIZE);
 
 			ALIGNOF_SHORT     = n.get(IDX_ALIGNOF_SHORT);