Create the m4 directory, and also place .gitignore in there for libtool.

patch by Jan Engelhardt (jengelh at medozas dot de)

Fixes the error:
aclocal: couldn't open directory "m4": No such file or directory
autoreconf: aclocal failed with exit status: 1

Change-Id: I1c1cd2c3d96f0d7d25616ec084dfc9bf9077fd4f
diff --git a/m4/.gitignore b/m4/.gitignore
new file mode 100644
index 0000000..64d9bbc
--- /dev/null
+++ b/m4/.gitignore
@@ -0,0 +1,2 @@
+/libtool.m4
+/lt*.m4