chdir-long, cycle-check, savewd: better 'inline'

chdir-long, cycle-check, savewd: better 'inline'

* lib/chdir-long.c (cdb_init, cdb_fchdir, cdb_free)
(find_non_slash):
* lib/cycle-check.c (is_zero_or_power_of_two):
* lib/savewd.c (savewd_delegating):
Change 'static inline' to 'inline'.
* lib/savewd.c, lib/savewd.h (SAVEWD_INLINE): New macro.
Replace all remaining uses of 'static inline' with it.
* lib/savewd.h:
Use _GL_INLINE_HEADER_BEGIN, _GL_INLINE_HEADER_END.
* m4/chdir-long.m4 (gl_PREREQ_CHDIR_LONG):
* m4/cycle-check.m4 (gl_CYCLE_CHECK):
* m4/savewd.m4 (gl_SAVEWD):
Do not require AC_C_INLINE.
* modules/savewd (Depends-on): Add extern-inline.