Update contrib + libgomp ChangeLogs for failed reject-commit testing

Update contrib + libgomp ChangeLogs for failed reject-commit testing

The following commit should have enabled checking for invalid revert hashes;
it worked locally - but did work as pre-commit hook on sourceware
as it wasn't copied to the hook directory:
r14-3777-gff20bce9f58 contrib/gcc-changelog: Check whether revert-commit exists

Hence, the following revert commit was wrongly applied:
r14-3778-gfbbd9001e9b Revert "contrib/gcc-changelog: Check whether revert-commit exists"
(In this commit: contrib/ChangeLog update for the revert.)

r14-3779-g69e83181ebc contrib/gcc-changelog: Check whether revert-commit exists
Re-applied the commit with a commit-log typo fixed but missing a late commit.

r14-3780-g1b0934b7276 Revert "contrib/gcc-changelog: Check whether revert-commit exists"
This commit still came through but re-instated the late wording fix in
contrib/gcc-changelog/git_commit.py.
(In this commit: contrib/ChangeLog update for the wording change.)

r14-3781-gd22cd7745ff Revert: "Another revert test with a bogus hash"
Another attempt to get a reject, but it still came through.
It removed tailing whitespace in libgomp/target.c
(In this commit: libgomp/ChangeLog was for the whitespace removal.)