treewide: NIX_*_COMPILE -> string

pkgs/servers/http/nginx/generic.nix

@@ -73,10 +73,10 @@ stdenv.mkDerivation {
     ++ optional (with stdenv.hostPlatform; isLinux || isFreeBSD) "--with-file-aio"
     ++ map (mod: "--add-module=${mod.src}") modules;
 
-  NIX_CFLAGS_COMPILE = [
+  NIX_CFLAGS_COMPILE = toString ([
     "-I${libxml2.dev}/include/libxml2"
     "-Wno-error=implicit-fallthrough"
-  ] ++ optional stdenv.isDarwin "-Wno-error=deprecated-declarations";
+  ] ++ optional stdenv.isDarwin "-Wno-error=deprecated-declarations");
 
   configurePlatforms = [];