main/editline: Add .gitignore.

This patch adds a .gitignore for main/editline to ignore all build results.

Change-Id: I68c7bf375ea46282689e5a706534b69fca233b5d
(cherry picked from commit 5d34bce6)

main/editline/.gitignore

+*.o_a
+Makefile
+common.h
+config.cache
+config.h
+editline.c
+emacs.h
+fcns.c
+fcns.h
+help.c
+help.h
+makelist
+vi.h