Add .clang-format file to third_party/subzero

This helps to keep the current formatting used by the Subzero codebase.

Bug: b/142132927
Change-Id: I8cb37860cf535e5b0c059316e66c19ddbafafc90
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/37271
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Tested-by: Antonio Maiorano <amaiorano@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
diff --git a/third_party/subzero/.clang-format b/third_party/subzero/.clang-format
new file mode 100644
index 0000000..5c85b31
--- /dev/null
+++ b/third_party/subzero/.clang-format
@@ -0,0 +1,3 @@
+---
+Language:        Cpp
+# BasedOnStyle:  LLVM