stdenv: Fix gcc multi line libc-cflags

which broke at least libstdc++5.

Closes #79761

pkgs/build-support/cc-wrapper/default.nix

@@ -361,7 +361,11 @@ stdenv.mkDerivation {
       done
     ''
 
+    # There are a few tools (to name one libstdcxx5) which do not work
+    # well with multi line flags, so make the flags single line again
     + ''
+      substituteInPlace $out/nix-support/libc-cflags --replace $'\n' ' '
+
       substituteAll ${./add-flags.sh} $out/nix-support/add-flags.sh
       substituteAll ${./add-hardening.sh} $out/nix-support/add-hardening.sh
       substituteAll ${../wrapper-common/utils.bash} $out/nix-support/utils.bash