[gardening] Fix multi-line comment gcc warning.

Fixes https://github.com/dart-lang/sdk/issues/59811
TEST=ci

Change-Id: I12e8b97189b5d4621812030f6360cbb56b61f27f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/402441
Commit-Queue: Alexander Aprelev <aam@google.com>
Reviewed-by: Brian Quinlan <bquinlan@google.com>

runtime/bin/socket_base.h

@@ -94,7 +94,7 @@ class SocketAddress {
   char as_string_[kMaxUnixPathLength];
 #else
   char as_string_[INET6_ADDRSTRLEN];
-#endif  // defined(DART_HOST_OS_LINUX) || defined(DART_HOST_OS_MACOS) ||       \
+#endif  // defined(DART_HOST_OS_LINUX) || defined(DART_HOST_OS_MACOS) ||
         // defined(DART_HOST_OS_ANDROID)
   RawAddr addr_;