Fix a few typos in comments

Apply the following spelling fixes:
$ git grep -F -l 'relevent' |
  xargs sed -i 's/relevent/relevant/g'
$ git grep -F -l 'checked fot' |
  xargs sed -i 's/checked fot/checked for/g'
$ git grep -F -l "could't" |
  xargs sed -i "s/could't/couldn't/g"
$ git grep -F -l 'wheter' | grep -Fv ChangeLog.old |
  xargs sed -i 's/wheter/whether/g'
$ git grep -F -l 'neccessary' | grep -Fv ChangeLog.old |
  xargs sed -i 's/neccessary/necessary/g'
$ git grep -F -l 'ouput' |
  xargs sed -i 's/ouput/output/g'
$ git grep -F -w -l 'iput' |
  xargs sed -i 's/iput/input/g'

This is inspired by a gnulib bug report at
https://lists.gnu.org/archive/html/bug-gnulib/2019-01/msg00081.html

* argp/argp-help.c: Fix typo in comment.
* misc/sys/cdefs.h: Likewise.
* posix/regexec.c (sift_states_iter_mb): Likewise.
* socket/sockatmark.c: Likewise.
* socket/sys/socket.h: Likewise.
* sysdeps/ia64/fpu/libm_sincos_large.S: Likewise.
* sysdeps/ia64/fpu/libm_sincosl.S: Likewise.
* sysdeps/ia64/fpu/s_cosl.S: Likewise.
* sysdeps/ieee754/dbl-64/k_rem_pio2.c: Likewise.
* sysdeps/unix/sockatmark.c: Likewise.
* time/strptime_l.c: Likewise.

1 files changed, 1 insertions, 1 deletions

diff --git a/misc/sys/cdefs.h b/misc/sys/cdefs.h
index d1f5fe208d..88bc7ac942 100644
--- a/misc/sys/cdefs.h
+++ b/misc/sys/cdefs.h
@@ -337,7 +337,7 @@
    semantics.
 
    clang++ identifies itself as gcc-4.2, but has support for GNU inlining
-   semantics, that can be checked fot by using the __GNUC_STDC_INLINE_ and
+   semantics, that can be checked for by using the __GNUC_STDC_INLINE_ and
    __GNUC_GNU_INLINE__ macro definitions.  */
 #if (!defined __cplusplus || __GNUC_PREREQ (4,3) \
      || (defined __clang__ && (defined __GNUC_STDC_INLINE__ \