wrapCCWith: structured argument for wrapper flags

Take a "nixSupport" argument that is an attrset of lists to append
to "$out/nix-support/${name}" where name is the name of the
attribute. This attrset is available from the passthru of the
wrapped compiler.

This is an alternative to imperatively issuing flags with
extraBuildCommands and makes it possible to append or filter
flags with an override.

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

@@ -14,6 +14,7 @@
 , nativeTools, noLibc ? false, nativeLibc, nativePrefix ? ""
 , propagateDoc ? cc != null && cc ? man
 , extraTools ? [], extraPackages ? [], extraBuildCommands ? ""
+, nixSupport ? {}
 , isGNU ? false, isClang ? cc.isClang or false, gnugrep ? null
 , buildPackages ? {}
 , libcxx ? null
@@ -155,6 +156,8 @@ stdenv.mkDerivation {
             (setenv "NIX_CFLAGS_COMPILE_${suffixSalt}" (concat (getenv "NIX_CFLAGS_COMPILE_${suffixSalt}") " -isystem " arg "/include"))))
         '(${concatStringsSep " " (map (pkg: "\"${pkg}\"") pkgs)}))
     '';
+
+    inherit nixSupport;
   };
 
   dontBuild = true;
@@ -521,7 +524,11 @@ stdenv.mkDerivation {
     ##
     ## Extra custom steps
     ##
-    + extraBuildCommands;
+    + extraBuildCommands
+    + lib.strings.concatStringsSep "; "
+      (lib.attrsets.mapAttrsToList
+        (name: value: "echo ${toString value} >> $out/nix-support/${name}")
+        nixSupport);
 
   inherit expand-response-params;
 

pkgs/top-level/all-packages.nix

@@ -13932,6 +13932,7 @@ with pkgs;
       # default.
       libcxx ? null
     , extraPackages ? lib.optional (cc.isGNU or false && stdenv.targetPlatform.isMinGW) threadsCross
+    , nixSupport ? {}
     , ...
     } @ extraArgs:
       callPackage ../build-support/cc-wrapper (let self = {
@@ -13943,7 +13944,7 @@ with pkgs;
     isGNU = cc.isGNU or false;
     isClang = cc.isClang or false;
 
-    inherit cc bintools libc libcxx extraPackages zlib;
+    inherit cc bintools libc libcxx extraPackages nixSupport zlib;
   } // extraArgs; in self);
 
   wrapCC = cc: wrapCCWith {