Introduce clang-format

An automated and opinionated style for code. We can decide to change the
style and have the source updated by the clang-format tool by running:

    make format

I've based the style on the Google style with exceptions to better
match
the current source style.

Change-Id: I43f85c7d4ce02ca999805558b25fcab2e43859c6
diff --git a/inc/alloc.h b/inc/alloc.h
index 4277495..4570b1a 100644
--- a/inc/alloc.h
+++ b/inc/alloc.h
@@ -9,4 +9,4 @@
 void *halloc_aligned(size_t size, size_t align);
 void *halloc_aligned_nosync(size_t size, size_t align);
 
-#endif  /* _ALLOC_H */
+#endif /* _ALLOC_H */