apple-sdk: add hack for C++ issues on x86_64-darwin (#397398)

pkgs/by-name/ap/apple-sdk/common/process-stubs.nix

@@ -35,7 +35,24 @@ self: super: {
           | .main_library.reexported_libraries[].names[] |= select([.] | inside($libs) | not)
         ' > usr/lib/$libSystem~
         # Convert libSystem back to tbd-v4 because not all tooling supports the JSON-based format yet.
-        llvm-readtapi -delete-input --filetype=tbd-v4 usr/lib/$libSystem~ -o usr/lib/$libSystem
+        llvm-readtapi --filetype=tbd-v4 usr/lib/$libSystem~ -o usr/lib/$libSystem
+        rm usr/lib/$libSystem~
       done
+
+      # Strip weak C++ symbols to work around `libc++` leakage in system
+      # frameworks for now. These are only present on `x86_64-darwin`, so
+      # it should hopefully be harmless.
+      #
+      # TODO FIXME: This is kind of horrible.
+      while read -r -d "" stub; do
+        printf 'Stripping weak C++ symbols from %s\n' "$stub"
+        llvm-readtapi --filetype=tbd-v5 "$stub" \
+        | jq '
+          (.main_library, .libraries[]?).exported_symbols[]?.data.weak[]? |=
+            select(startswith("__Z") | not)
+        ' > $stub~
+        llvm-readtapi --filetype=tbd-v4 $stub~ -o $stub
+        rm $stub~
+      done < <(find . -name '*.tbd' -print0)
     '';
 }

pkgs/development/libraries/opencv/4.x.nix

@@ -88,7 +88,6 @@
   enabledModules ? [ ],
 
   bzip2,
-  apple-sdk_14, # earlier SDKs cause linking issues on x86_64
   callPackage,
 }@inputs:
 
@@ -417,7 +416,6 @@ effectiveStdenv.mkDerivation {
     ]
     ++ optionals effectiveStdenv.hostPlatform.isDarwin [
       bzip2
-      apple-sdk_14
     ]
     ++ optionals enableDocs [
       doxygen

pkgs/development/libraries/qt-5/modules/qtbase.nix

@@ -88,7 +88,6 @@ let
       throw "Please add a qtPlatformCross entry for ${plat.config}";
 
   # Per https://doc.qt.io/qt-5/macos.html#supported-versions: build SDK = 13.x or 14.x.
-  # SDK 13.x causes weird linking errors on x86_64-darwin, so use 14.x
   darwinVersionInputs = [
     apple-sdk_14
   ];