Merge branch 'tg/add-chmod+x-fix' into maint

"git add --chmod=+x <pathspec>" added recently only toggled the
executable bit for paths that are either new or modified. This has
been corrected to flip the executable bit for all paths that match
the given pathspec.

* tg/add-chmod+x-fix:
t3700-add: do not check working tree file mode without POSIXPERM
t3700-add: create subdirectory gently
add: modify already added files when --chmod is given
read-cache: introduce chmod_index_entry
update-index: add test for chmod flags

diff --cc builtin/checkout.c
Simple merge

diff --cc builtin/commit.c
Simple merge

diff --cc builtin/update-index.c
Simple merge

diff --cc cache.h
Simple merge

diff --cc read-cache.c
Simple merge