Remove auto-generated files and add them to .gitignore.

* .gitignore: Add files generated by autoreconf -vif.
* Makefile.in, aclocal.m4, compile, config.guess, config.sub,
configure, depcomp, include/private/config.h.in, install-sh,
ltmain.sh, m4/libtool.m4, m4/ltoptions.m4, m4/ltsugar.m4,
m4/ltversion.m4, m4/lt~obsolete.m4, missing, mkinstalldirs: Remove.

.gitignore

@@ -42,6 +42,26 @@
 /include/private/config.h.in~
 /include/private/stamp-h1
 
+# These files are generated by autoreconf:
+/Makefile.in
+/aclocal.m4
+/autom4te.cache/
+/compile
+/config.guess
+/config.sub
+/configure
+/depcomp
+/include/private/config.h.in
+/install-sh
+/ltmain.sh
+/m4/libtool.m4
+/m4/ltoptions.m4
+/m4/ltsugar.m4
+/m4/ltversion.m4
+/m4/lt~obsolete.m4
+/missing
+/mkinstalldirs
+
 # Rarely generated files (mostly by some Win/DOS compilers):
 /*.bsc
 /*.csm