add autom4te.cache/ to .gitignore

Add missing "autom4te.cache/" to .gitignore file.

Tested: Not tested on hardware.
Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: Ie06d1b22bb2a74e2f6e2901d213fffa0cacac2c4
diff --git a/.gitignore b/.gitignore
index 1b62050..04eba2e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -39,6 +39,7 @@
 *.so.*
 
 # Autotools
+autom4te.cache/
 .deps
 .dirstamp
 .libs