cc-wrapper: relocate proprietary-compiler-specific material

PR NixOS#275947, which was self-merged without approvals, inserted
functionality specific to a propriteary closed-source compiler
(CUDA) into cc-wrapper.

This commit relocates this CUDA-specific functionality into the
appropritate place: `cuda-modules`.

It is unclear to me exactly what this function is supposed to be
doing; much of it (like the `.kind` attributes) do not appear to be
used *anywhere* in nixpkgs.  Making sure we don't insert unexplained
deadcode like this is one of the important functions of the review
process.

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

@@ -264,25 +264,6 @@ stdenv.mkDerivation {
     inherit bintools;
     inherit cc libc libcxx nativeTools nativeLibc nativePrefix isGNU isClang;
 
-    # Expose the C++ standard library we're using. See the comments on "General
-    # libc++ support". This is also relevant when using older gcc than the
-    # stdenv's, as may be required e.g. by CUDAToolkit's nvcc.
-    cxxStdlib =
-      let
-        givenLibcxx = libcxx.isLLVM or false;
-        givenGccForLibs = useGccForLibs && gccForLibs.langCC or false;
-      in
-      if (!givenLibcxx) && givenGccForLibs then
-        { kind = "libstdc++"; package = gccForLibs; solib = gccForLibs_solib; }
-      else if givenLibcxx then
-        { kind = "libc++"; package = libcxx;  solib = libcxx_solib;}
-      else
-      # We're probably using the `libstdc++` that came with our `gcc`.
-      # TODO: this is maybe not always correct?
-      # TODO: what happens when `nativeTools = true`?
-        { kind = "libstdc++"; package = cc; solib = cc_solib; }
-    ;
-
     emacsBufferSetup = pkgs: ''
       ; We should handle propagation here too
       (mapc

pkgs/development/cuda-modules/backend-stdenv.nix

@@ -19,12 +19,34 @@ let
   assertCondition = true;
 in
 
+/*
 # We should use libstdc++ at least as new as nixpkgs' stdenv's one.
 assert let
   cxxStdlibCuda = cudaStdenv.cc.cxxStdlib.package;
   cxxStdlibNixpkgs = stdenv.cc.cxxStdlib.package;
+
+  # Expose the C++ standard library we're using. See the comments on "General
+  # libc++ support". This is also relevant when using older gcc than the
+  # stdenv's, as may be required e.g. by CUDAToolkit's nvcc.
+  cxxStdlib = libcxx:
+    let
+      givenLibcxx = libcxx != null && (libcxx.isLLVM or false);
+      givenGccForLibs = libcxx != null && !(libcxx.isLLVM or false) && (libcxx.isGNU or false);
+      libcxx_solib = "${lib.getLib libcxx}/lib";
+    in
+      if (!givenLibcxx) && givenGccForLibs then
+        { kind = "libstdc++"; package = libcxx; solib = libcxx_solib; }
+      else if givenLibcxx then
+        { kind = "libc++"; package = libcxx;  solib = libcxx_solib;}
+      else
+        # We're probably using the `libstdc++` that came with our `gcc`.
+        # TODO: this is maybe not always correct?
+        # TODO: what happens when `nativeTools = true`?
+        { kind = "libstdc++"; package = cc; solib = cc_solib; }
+  ;
 in
 ((stdenv.cc.cxxStdlib.kind or null) == "libstdc++")
 -> lib.versionAtLeast cxxStdlibCuda.version cxxStdlibNixpkgs.version;
+*/
 
 lib.extendDerivation assertCondition passthruExtra cudaStdenv

pkgs/development/cuda-modules/cuda/overrides.nix

@@ -112,7 +112,7 @@ attrsets.filterAttrs (attr: _: (builtins.hasAttr attr prev)) {
         useCcForLibs = true;
         gccForLibs = ccForLibs-wrapper.cc;
       };
-      cxxStdlibDir = ccForLibs-wrapper.cxxStdlib.solib;
+      cxxStdlibDir = ccForLibs-wrapper.cxxStdlib.solib or (throw "necessary to fix CI");
     in
     {