fflush, stat: no 'static inline'

fflush, stat: no 'static inline'

* lib/fflush.c (clear_ungetc_buffer_preserving_position)
(clear_ungetc_buffer, disable_seek_optimization)
(restore_seek_optimization, update_fpos_cache):
* lib/stat.c (orig_stat):
Now static, not static inline.
* lib/fflush.c (disable_seek_optimization, restore_seek_optimization)
(update_fpos_cache):
Define only if ! (defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1).
* m4/fflush.m4 (gl_PREREQ_FFLUSH):
* m4/stat.m4 (gl_PREREQ_STAT):
Do not require AC_C_INLINE.