gitignore: add new pieces from build

Since adding new build folders, add the corresponding items to the
gitignore.

Change-Id: I3f880ea7204877dbe0e9bad227d0008235f8cd3e
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/.gitignore b/.gitignore
index dbd5f0a..a4aeb3a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -16,6 +16,7 @@
 /autoscan.log
 /autoscan-*.log
 /aclocal.m4
+/build-aux
 /compile
 /config.guess
 /config.h.in
@@ -24,6 +25,7 @@
 /configure.scan
 /depcomp
 /install-sh
+/m4
 /missing
 /stamp-h1