Add .gitignore.

.gitignore

@@ -0,0 +1,43 @@
+# http://www.gnu.org/software/automake
+
+Makefile.in
+/ar-lib
+/mdate-sh
+/py-compile
+/test-driver
+/ylwrap
+
+# http://www.gnu.org/software/autoconf
+
+autom4te.cache
+/autoscan.log
+/autoscan-*.log
+/aclocal.m4
+/compile
+/config.guess
+/config.h.in
+/config.log
+/config.status
+/config.sub
+/configure
+/configure.scan
+/depcomp
+/install-sh
+/missing
+/stamp-h1
+
+# https://www.gnu.org/software/libtool/
+
+/ltmain.sh
+
+# 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