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

runtime/platform/utils_linux.h

 // Copyright (c) 2012, 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_UTILS_LINUX_H_
 #define RUNTIME_PLATFORM_UTILS_LINUX_H_
 
 #include <endian.h>  // NOLINT
 
 namespace dart {
@@ skipping 44 matching lines @@
   return htole32(value);
 }
 
 
 inline uint64_t Utils::HostToLittleEndian64(uint64_t value) {
   return htole64(value);
 }
 
 
 inline char* Utils::StrError(int err, char* buffer, size_t bufsize) {
-#if !defined(__GLIBC__) ||                                              \
-((_POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600) && !_GNU_SOURCE)
+#if !defined(__GLIBC__) ||                                                     \
+    ((_POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600) && !_GNU_SOURCE)
   // Use the XSI version.
   if (strerror_r(err, buffer, bufsize) != 0) {
     snprintf(buffer, bufsize, "%s", "strerror_r failed");
   }
   return buffer;
 #else
   // Use the GNU specific version.
   return strerror_r(err, buffer, bufsize);
 #endif
 }
 
 }  // namespace dart
 
 #endif  // RUNTIME_PLATFORM_UTILS_LINUX_H_