Add .clang-format and run clang-format on runtime/platform.

runtime/platform/memory_sanitizer.h

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef RUNTIME_PLATFORM_MEMORY_SANITIZER_H_
 #define RUNTIME_PLATFORM_MEMORY_SANITIZER_H_
 
 #include "platform/globals.h"
 
 // Allow the use of Msan (MemorySanitizer). This is needed as Msan needs to be
 // told about areas that are initialized by generated code.
 #if defined(__has_feature)
 #if __has_feature(memory_sanitizer)
-extern "C" void __msan_unpoison(void *, size_t);
+extern "C" void __msan_unpoison(void*, size_t);
 #define MSAN_UNPOISON(ptr, len) __msan_unpoison(ptr, len)
 #define NO_SANITIZE_MEMORY __attribute__((no_sanitize_memory))
 #else  // __has_feature(memory_sanitizer)
-#define MSAN_UNPOISON(ptr, len) do {} while (false && (ptr) == 0 && (len) == 0)
+#define MSAN_UNPOISON(ptr, len)                                                \
+  do {                                                                         \
+  } while (false && (ptr) == 0 && (len) == 0)
 #define NO_SANITIZE_MEMORY
 #endif  // __has_feature(memory_sanitizer)
-#else  // defined(__has_feature)
-#define MSAN_UNPOISON(ptr, len) do {} while (false && (ptr) == 0 && (len) == 0)
+#else   // defined(__has_feature)
+#define MSAN_UNPOISON(ptr, len)                                                \
+  do {                                                                         \
+  } while (false && (ptr) == 0 && (len) == 0)
 #define NO_SANITIZE_MEMORY
 #endif  // defined(__has_feature)
 
 #endif  // RUNTIME_PLATFORM_MEMORY_SANITIZER_H_