This time rebuilding (at least without removing stuff) does not help. r238934 lib/libWebCoreGTK.a(lib/../Source/WebCore/CMakeFiles/WebCore.dir/__/__/DerivedSources/WebCore/unified-sources/UnifiedSource370.cpp.o):UnifiedSource370.cpp:function WebCore::RenderLayer::name() const: error: undefined reference to 'WTF::StringBuilder::append(char16_t const*, unsigned int)' lib/libWebCoreGTK.a(lib/../Source/WebCore/CMakeFiles/WebCore.dir/__/__/DerivedSources/WebCore/unified-sources/UnifiedSource370.cpp.o):UnifiedSource370.cpp:function WebCore::RenderLayer::name() const: error: undefined reference to 'WTF::StringBuilder::append(char16_t const*, unsigned int)' lib/libWebCoreGTK.a(lib/../Source/WebCore/CMakeFiles/WebCore.dir/__/__/DerivedSources/WebCore/unified-sources/UnifiedSource370.cpp.o):UnifiedSource370.cpp:function WebCore::RenderLayer::name() const: error: undefined reference to 'WTF::StringBuilder::append(char16_t const*, unsigned int)' collect2: error: ld returned 1 exit status ninja: build stopped: subcommand failed.