.gitignore: add autom4te.cache

Add autom4te.cache to .gitignore file.

Change-Id: I4b246860edc94dd31e844badc7ddfa54febe50fb
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/.gitignore b/.gitignore
index ae38b8a..9d66280 100644
--- a/.gitignore
+++ b/.gitignore
@@ -19,6 +19,7 @@
 .dirstamp
 .libs
 /aclocal.m4
+/autom4te.cache
 /build-aux
 /config.h
 /config.h.in