Rename CACHE_LINE_SIZE to PG_CACHE_LINE_SIZE.

As noted in http://bugs.debian.org/763098 there is a conflict between
postgres' definition of CACHE_LINE_SIZE and the definition by various
*bsd platforms. It's debatable who has the right to define such a
name, but postgres' use was only introduced in 375d8526f2 (9.4), so
it seems like a good idea to rename it.

Discussion: 20140930195756.GC27407@msg.df7cb.de

Per complaint of Christoph Berg in the above email, although he's not
the original bug reporter.

Backpatch to 9.4 where the define was introduced.

src/backend/access/transam/xlog.c

@@ -409,7 +409,7 @@ typedef struct
 typedef union WALInsertLockPadded
 {
 	WALInsertLock l;
-	char		pad[CACHE_LINE_SIZE];
+	char		pad[PG_CACHE_LINE_SIZE];
 } WALInsertLockPadded;
 
 /*
@@ -436,7 +436,7 @@ typedef struct XLogCtlInsert
 	 * read on every WAL insertion, but updated rarely, and we don't want
 	 * those reads to steal the cache line containing Curr/PrevBytePos.
 	 */
-	char		pad[CACHE_LINE_SIZE];
+	char		pad[PG_CACHE_LINE_SIZE];
 
 	/*
 	 * fullPageWrites is the master copy used by all backends to determine

src/include/pg_config_manual.h

@@ -238,7 +238,7 @@
  * bytes of wasted memory. The default is 128, which should be large enough
  * for all supported platforms.
  */
-#define CACHE_LINE_SIZE		128
+#define PG_CACHE_LINE_SIZE		128
 
 /*
  *------------------------------------------------------------------------