[REG 6.3.1->6.4.0] WebEngine not compiling on macOS10.15 or macOS11

 cmake -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++ -DQT_BUILD_EXAMPLES=OFF -DCMAKE_BUILD_TYPE=Release -DFEATURE_separate_debug_info=OFF -DFEATURE_headersclean=ON -DFEATURE_framework=ON -DODBC_ROOT=/usr/local/opt/libiodbc -DPostgreSQL_ROOT=/Applications/Postgres.app/Contents/Versions/9.6/bin/.. -DQT_BUILD_TESTS=OFF /Users/qt/RTA/src-6.4.0 -DCMAKE_INSTALL_PREFIX:PATH=/Users/qt/RTA/src-6.4.0/qtbase

[22913/27134] CXX obj/third_party/blink/renderer/platform/heap/heap/heap_jumbo_1.o
FAILED: obj/third_party/blink/renderer/platform/heap/heap/heap_jumbo_1.o 
../../../../../../../../Applications/Xcode12.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang++ -MMD -MF obj/third_party/blink/renderer/platform/heap/heap/heap_jumbo_1.o.d -DOFFICIAL_BUILD -DTOOLKIT_QT -D_LIBCPP_HAS_NO_ALIGNED_ALLOCATION -DCR_XCODE_VERSION=1240 -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__ASSERT_MACROS_DEFINE_VERSIONS_WITHOUT_UNDERSCORES=0 -DNDEBUG -DNVALGRIND -DDYNAMIC_ANNOTATIONS_ENABLED=0 -DBLINK_IMPLEMENTATION=1 -DINSIDE_BLINK -DBLINK_PLATFORM_IMPLEMENTATION=1 -DWEBP_EXTERN=extern -DUSE_EGL -DSK_UNTIL_CRBUG_1187654_IS_FIXED -DSK_WIN_FONTMGR_NO_SIMULATIONS -DSK_EXPERIMENTAL_ADD_ATLAS_PADDING -DSK_CODEC_DECODES_PNG -DSK_CODEC_DECODES_WEBP -DSK_ENCODE_PNG -DSK_ENCODE_WEBP -DSK_ENABLE_SKSL -DSK_USER_CONFIG_HEADER=\"../../skia/config/SkUserConfig.h\" -DSK_GL -DSK_CODEC_DECODES_JPEG -DSK_ENCODE_JPEG -DSK_HAS_WUFFS_LIBRARY -DSK_SUPPORT_GPU=1 -DSK_GPU_WORKAROUNDS_HEADER=\"gpu/config/gpu_driver_bug_workaround_autogen.h\" -DSK_BUILD_FOR_MAC 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-I../../../3rdparty/chromium/third_party/ced/src -I../../../3rdparty/chromium/third_party/webrtc_overrides -I../../../3rdparty/chromium/third_party/webrtc -Igen/third_party/webrtc -I../../../3rdparty/chromium/third_party/mesa_headers -I../../../3rdparty/chromium/third_party/libwebm/source -I../../../3rdparty/chromium/third_party/leveldatabase -I../../../3rdparty/chromium/third_party/leveldatabase/src -I../../../3rdparty/chromium/third_party/leveldatabase/src/include -I../../../3rdparty/chromium/third_party/libjpeg_turbo -I../../../3rdparty/chromium/third_party/iccjpeg -I../../../3rdparty/chromium/third_party/libpng -I../../../3rdparty/chromium/third_party/zlib -I../../../3rdparty/chromium/third_party/ots/src/include -fno-delete-null-pointer-checks -fno-ident -fno-strict-aliasing -fstack-protector -Wno-unknown-argument -Wno-unknown-attributes -Wno-unknown-warning-option -Wno-unknown-pragmas -fcolor-diagnostics -fmerge-all-constants -arch x86_64 -Wall -Wextra -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 -Wimplicit-fallthrough -Wthread-safety -Wextra-semi -Wunguarded-availability -Wno-missing-field-initializers -Wno-unused-parameter -Wloop-analysis -Wno-unneeded-internal-declaration -Wenum-compare-conditional -Wno-psabi -Wno-ignored-pragma-optimize -Wshadow -fno-omit-frame-pointer -isysroot ../../../../../../../../Applications/Xcode12.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.1.sdk -mmacosx-version-min=10.14 -fvisibility=hidden -Wheader-hygiene -Wstring-conversion -Wtautological-overlap-compare -Wexit-time-destructors -Wno-unused-variable -Wconversion -Wno-float-conversion -Wno-sign-conversion -Wno-implicit-float-conversion -Wno-implicit-int-conversion -Wno-unused-variable -Wglobal-constructors -Wno-unused-variable -Wconversion -Wno-float-conversion -Wno-sign-conversion -Wno-implicit-float-conversion -Wno-implicit-int-conversion -Wno-unused-variable -g0 -O2 -DPROTOBUF_ALLOW_DEPRECATED=1 -Wno-shadow -Wno-parentheses-equality -Wno-tautological-compare -Wno-thread-safety-attributes -Wno-undefined-bool-conversion -Wno-tautological-undefined-compare -std=c++17 -Wno-trigraphs -fno-aligned-new -stdlib=libc++ -fno-exceptions -fno-rtti -fvisibility-inlines-hidden -Wno-deprecated-declarations -include obj/third_party/blink/renderer/platform/heap/heap/precompile_platform.h-cc -c gen/third_party/blink/renderer/platform/heap/heap_jumbo_1.cc -o obj/third_party/blink/renderer/platform/heap/heap/heap_jumbo_1.o
In file included from gen/third_party/blink/renderer/platform/heap/heap_jumbo_1.cc:1:
In file included from /Users/qt/src-6.4.0-beta1/qtwebengine/src/core/Release/x86_64/../../../3rdparty/chromium/third_party/blink/renderer/platform/precompile_platform.h:21:
In file included from /Users/qt/src-6.4.0-beta1/qtwebengine/src/core/Release/x86_64/../../../3rdparty/chromium/third_party/blink/renderer/platform/heap/handle.h:38:
In file included from ../../../3rdparty/chromium/third_party/blink/renderer/platform/heap/member.h:12:
In file included from ../../../3rdparty/chromium/third_party/blink/renderer/platform/wtf/hash_functions.h:27:
/Users/qt/src-6.4.0-beta1/qtwebengine/src/core/Release/x86_64/../../../3rdparty/chromium/base/bit_cast.h:28:3: error: non-void constexpr function 'bit_cast' should return a value
  return __builtin_bit_cast(Dest, source);
  ^
../../../3rdparty/chromium/third_party/blink/renderer/platform/wtf/hash_functions.h:123:51: note: in instantiation of function template specialization 'bit_cast<unsigned int, float>' requested here
  static unsigned GetHash(T key) { return HashInt(bit_cast<Bits>(key)); }
                                                  ^
../../../3rdparty/chromium/third_party/blink/renderer/platform/wtf/hash_functions.h:186:40: note: in instantiation of member function 'WTF::FloatHash<float>::GetHash' requested here
  AddIntToHash(hash, FloatHash<float>::GetHash(value));
                                       ^
1 error generated.