[gn build] Port 1e77b39

Author: llvmgnsyncbot

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

@@ -81,6 +81,7 @@ if (current_toolchain == default_toolchain) {
       "__algorithm/generate.h",
       "__algorithm/generate_n.h",
       "__algorithm/half_positive.h",
+      "__algorithm/in_fun_result.h",
       "__algorithm/in_in_out_result.h",
       "__algorithm/in_in_result.h",
       "__algorithm/in_out_out_result.h",