Add clang-format file

Also run it across the whole tree to get everything using the One True Style.
We don't yet run this in an automated fashion as it's a little slow, but
there is a snippet to do so in makeall.sh.

LibC/errno.h

@@ -1,18 +1,18 @@
 #pragma once
 
-#include <sys/cdefs.h>
 #include <errno_numbers.h>
+#include <sys/cdefs.h>
 
 #define __RETURN_WITH_ERRNO(rc, good_ret, bad_ret) \
-    do { \
-        if (rc < 0) { \
-            errno = -rc; \
-            return (bad_ret); \
-        } else { \
-            errno = 0; \
-            return (good_ret); \
-        } \
-    } while(0)
+    do {                                           \
+        if (rc < 0) {                              \
+            errno = -rc;                           \
+            return (bad_ret);                      \
+        } else {                                   \
+            errno = 0;                             \
+            return (good_ret);                     \
+        }                                          \
+    } while (0)
 
 __BEGIN_DECLS