[gn build] Port 33de5a3

Author: llvmgnsyncbot

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

@@ -509,7 +509,7 @@ if (current_toolchain == default_toolchain) {
       "__fwd/bit_reference.h",
       "__fwd/complex.h",
       "__fwd/fstream.h",
-      "__fwd/hash.h",
+      "__fwd/functional.h",
       "__fwd/ios.h",
       "__fwd/istream.h",
       "__fwd/mdspan.h",