Update Autotools.gitignore

add files generated by the autotool m4.

Autotools.gitignore

@@ -31,3 +31,12 @@ Makefile.in
 # http://www.gnu.org/software/texinfo
 
 /texinfo.tex
+
+# http://www.gnu.org/software/m4/
+
+m4/libtool.m4
+m4/ltoptions.m4
+m4/ltsugar.m4
+m4/ltversion.m4
+m4/lt~obsolete.m4
+autom4te.cache