CHROMIUM: Ignore the top level build/ directory tree.

This tree is generated by gentoo tools and should be ignored by git.

Tested by observing that git does ignore the top level build/ tree,
but does report build/ subtrees within the kernel tree.

Review URL: http://codereview.chromium.org/2512002

Change-Id: Ic631c4f151f3ecaa1112b0129bf5841e9e1b3ba0

diff --git a/.gitignore b/.gitignore
index 0c39aa2..a097d2f 100644
--- a/.gitignore
+++ b/.gitignore

@@ -77,6 +77,9 @@
 include/generated
 arch/*/include/generated
 
+# kernelconfig build directory
+/build/
+
 # stgit generated dirs
 patches-*