[gn build] Port 40c07b5

Author: llvmgnsyncbot

llvm/utils/gn/secondary/libcxx/src/BUILD.gn

@@ -122,7 +122,6 @@ cxx_sources = [
   "condition_variable_destructor.cpp",
   "error_category.cpp",
   "exception.cpp",
-  "fstream.cpp",
   "functional.cpp",
   "future.cpp",
   "hash.cpp",
@@ -146,7 +145,6 @@ cxx_sources = [
   "iostream.cpp",
   "legacy_pointer_safety.cpp",
   "locale.cpp",
-  "ostream.cpp",
   "memory.cpp",
   "memory_resource.cpp",
   "mutex.cpp",
@@ -155,6 +153,7 @@ cxx_sources = [
   "new_handler.cpp",
   "new_helpers.cpp",
   "optional.cpp",
+  "ostream.cpp",
   "print.cpp",
   "random.cpp",
   "random_shuffle.cpp",