libsForQt5.qt5.qtwebengine: fix build with clang (#358759)

pkgs/development/libraries/qt-5/5.15/default.nix

@@ -176,6 +176,15 @@ let
       # See: https://bugreports.qt.io/browse/QTBUG-124375
       # Backport of: https://code.qt.io/cgit/qt/qtwebengine-chromium.git/commit/?id=a766045f65f934df3b5f1aa63bc86fbb3e003a09
       ./qtwebengine-ninja-1.12.patch
+      # 5.15.17: Fixes 'converts to incompatible function type [-Werror,-Wcast-function-type-strict]'
+      # in chromium harfbuzz dependency. This may be removed again if harfbuzz is updated
+      # to include the upstream fixes: https://github.com/harfbuzz/harfbuzz/commit/d88269c827895b38f99f7cf741fa60210d4d5169
+      # See https://trac.macports.org/ticket/70850
+      (fetchpatch {
+        url = "https://github.com/macports/macports-ports/raw/dd7bc40d8de48c762bf9757ce0a0672840c5d8c2/aqua/qt5/files/patch-qtwebengine_hb-ft.cc_error.diff";
+        sha256 = "sha256-8/CYjGM5n2eJ6sG+ODTa8fPaxZSDVyKuInpc3IlZuyc=";
+        extraPrefix = "";
+      })
     ] ++ lib.optionals stdenv.hostPlatform.isDarwin [
       ./qtwebengine-darwin-no-platform-check.patch
       ./qtwebengine-mac-dont-set-dsymutil-path.patch

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

@@ -173,6 +173,10 @@ qtModule ({
           "-march=westmere"
         ] ++ lib.optionals stdenv.cc.isClang [
           "-Wno-elaborated-enum-base"
+          # 5.15.17: need to silence these two warnings
+          # https://trac.macports.org/ticket/70850
+          "-Wno-enum-constexpr-conversion"
+          "-Wno-unused-but-set-variable"
         ]);
   } // lib.optionalAttrs (stdenv.buildPlatform != stdenv.hostPlatform) {
     NIX_CFLAGS_LINK = "-Wl,--no-warn-search-mismatch";