Add OpenCL build.

Bug: skia:8081
Change-Id: I8b2a88cc25970398511aa078d456ca8a1182792b
Reviewed-on: https://skia-review.googlesource.com/136594
Commit-Queue: Mike Klein <mtklein@google.com>
Auto-Submit: Ben Wagner <benjaminwagner@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
diff --git a/.gitignore b/.gitignore
index 0de0124..c9b9fcd 100644
--- a/.gitignore
+++ b/.gitignore
@@ -39,7 +39,7 @@
 tools/skp/page_sets/data/*.wpr
 xcodebuild
 
-build
+/build
 buildtools
 tools/clang
 third_party/llvm-build