[gn build] Port 17f0062

Author: llvmgnsyncbot

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

@@ -651,6 +651,8 @@ if (current_toolchain == default_toolchain) {
       "__numeric/transform_exclusive_scan.h",
       "__numeric/transform_inclusive_scan.h",
       "__numeric/transform_reduce.h",
+      "__ostream/basic_ostream.h",
+      "__ostream/print.h",
       "__pstl/backends/libdispatch.h",
       "__pstl/backends/serial.h",
       "__pstl/backends/std_thread.h",