build: mention GNU Emacs and Global tags as ignored by git (#3403)

Add TAGS (generated by 'etags' and used by GNU Emacs) and
ID / GPATH / GRTAGS / GTAGS / GSYMS (generated by GNU Global)
entries to .gitignore. Note the same set of generated files
is cleaned by 'distclean-tags' target from Makefile.in.

Signed-off-by: Dmitry Antipov <dantipov@cloudlinux.com>
Updates: #1000

.gitignore

@@ -5,6 +5,12 @@ config.*
 configure
 cscope.*
 tags
+TAGS
+ID
+GPATH
+GRTAGS
+GTAGS
+GSYMS
 depcomp
 INSTALL
 install-sh