reverse definition dependency between PAGESIZE and PAGE_SIZE

PAGESIZE is actually the version defined in POSIX base, with PAGE_SIZE
being in the XSI option. use PAGESIZE as the underlying definition to
facilitate making exposure of PAGE_SIZE conditional.

arch/i386/bits/limits.h

 #if defined(_POSIX_SOURCE) || defined(_POSIX_C_SOURCE) \
  || defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
-#define PAGE_SIZE 4096
+#define PAGESIZE 4096
 #define LONG_BIT 32
 #endif
 

arch/or1k/bits/limits.h

 #if defined(_POSIX_SOURCE) || defined(_POSIX_C_SOURCE) \
  || defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
-#define PAGE_SIZE 8192
+#define PAGESIZE 8192
 #define LONG_BIT 32
 #endif
 

arch/s390x/bits/limits.h

 #if defined(_POSIX_SOURCE) || defined(_POSIX_C_SOURCE) \
  || defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
-#define PAGE_SIZE 4096
+#define PAGESIZE 4096
 #define LONG_BIT 64
 #endif
 

arch/sh/bits/limits.h

 #if defined(_POSIX_SOURCE) || defined(_POSIX_C_SOURCE) \
  || defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
-#define PAGE_SIZE 4096
+#define PAGESIZE 4096
 #define LONG_BIT 32
 #endif
 

arch/x32/bits/limits.h

 #if defined(_POSIX_SOURCE) || defined(_POSIX_C_SOURCE) \
  || defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
-#define PAGE_SIZE 4096
+#define PAGESIZE 4096
 #define LONG_BIT 32
 #endif
 

arch/x86_64/bits/limits.h

 #if defined(_POSIX_SOURCE) || defined(_POSIX_C_SOURCE) \
  || defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
-#define PAGE_SIZE 4096
+#define PAGESIZE 4096
 #define LONG_BIT 64
 #endif
 

include/limits.h

@@ -40,8 +40,8 @@
  || defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
 
 #define PIPE_BUF 4096
-#ifdef PAGE_SIZE
-#define PAGESIZE PAGE_SIZE
+#ifdef PAGESIZE
+#define PAGE_SIZE PAGESIZE
 #endif
 #define FILESIZEBITS 64
 #define NAME_MAX 255