version: fix builtin linking & documentation

Like most builtins, 'version' is documented in a corresponding
'Documentation/git-version.txt' and can be invoked with 'git version'.
However, the 'check-docs' Makefile target showed that it was "removed but
documented: git-version." This was cause by the fact that it is not built as
a standalone 'git-version' executable, therefore appearing "removed" to
'check-docs'.

Without a precedent for documented builtins that aren't built into an
executable *or* any clear reason why a standalone 'git-version' shouldn't
exist, the 'check-docs' error appears to correctly identify an issue. To
correct that mismatch, add 'git-version' to the 'BUILT_INS' list in the root
Makefile (indicating that the 'cmd_version()' function appears in a file
that is *not* 'builtin/version.c'). Additionally, to avoid the "no link"
message in 'check-docs', list 'git-version' as an "ancilliaryinterrogator"
(like 'git help') in 'command-list.txt'.

Signed-off-by: Victoria Dye <vdye@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

.gitignore

@@ -181,6 +181,7 @@
 /git-verify-commit
 /git-verify-pack
 /git-verify-tag
+/git-version
 /git-web--browse
 /git-whatchanged
 /git-worktree

Makefile

@@ -818,6 +818,7 @@ BUILT_INS += git-show$X
 BUILT_INS += git-stage$X
 BUILT_INS += git-status$X
 BUILT_INS += git-switch$X
+BUILT_INS += git-version$X
 BUILT_INS += git-whatchanged$X
 
 # what 'all' will build but not install in gitexecdir

command-list.txt

@@ -199,6 +199,7 @@ git-var                                 plumbinginterrogators
 git-verify-commit                       ancillaryinterrogators
 git-verify-pack                         plumbinginterrogators
 git-verify-tag                          ancillaryinterrogators
+git-version                             ancillaryinterrogators
 git-whatchanged                         ancillaryinterrogators          complete
 git-worktree                            mainporcelain
 git-write-tree                          plumbingmanipulators