Promote off_t type when long->4-bytes and size_t->8-bytes

To guarantee that `off_t >= size_t`

As required to build  fmemopen.c line 117:
` _Static_assert(sizeof(off_t) >= sizeof(size_t), "must avoid truncation");`

https://github.com/picolibc/picolibc/blame/d44fa19886bad821f6004583c75bfc202cd4b156/newlib/libc/tinystdio/fmemopen.c#L117C14-L117C14

Signed-off-by: Abdallah Abdelhafeez <[email protected]>

Author: Abdallahs70

newlib/libc/include/sys/_types.h

@@ -78,8 +78,12 @@ typedef __uint32_t __fsfilcnt_t;
 #endif
 
 #ifndef __machine_off_t_defined
+#if __SIZEOF_SIZE_T__ == 8 && __SIZEOF_LONG__ < 8
+typedef __uint64_t _off_t;
+#else
 typedef long _off_t;
 #endif
+#endif
 
 #if defined(__XMK__)
 typedef signed char __pid_t;