[gn build] Port b049fc0

Author: llvmgnsyncbot

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

@@ -153,6 +153,7 @@ if (current_toolchain == default_toolchain) {
       "__algorithm/pstl_backends/cpu_backends/for_each.h",
       "__algorithm/pstl_backends/cpu_backends/serial.h",
       "__algorithm/pstl_backends/cpu_backends/transform.h",
+      "__algorithm/pstl_copy.h",
       "__algorithm/pstl_fill.h",
       "__algorithm/pstl_find.h",
       "__algorithm/pstl_for_each.h",