[gn build] Port 90670b5

Author: llvmgnsyncbot

llvm/utils/gn/secondary/llvm/lib/Support/BUILD.gn

@@ -176,6 +176,7 @@ static_library("Support") {
     "circular_raw_ostream.cpp",
     "raw_os_ostream.cpp",
     "raw_ostream.cpp",
+    "raw_ostream_proxy.cpp",
     "raw_socket_stream.cpp",
     "regcomp.c",
     "regerror.c",

llvm/utils/gn/secondary/llvm/unittests/Support/BUILD.gn

@@ -113,6 +113,7 @@ unittest("SupportTests") {
     "buffer_ostream_test.cpp",
     "formatted_raw_ostream_test.cpp",
     "raw_fd_stream_test.cpp",
+    "raw_ostream_proxy_test.cpp",
     "raw_ostream_test.cpp",
     "raw_pwrite_stream_test.cpp",
     "raw_sha1_ostream_test.cpp",