After upgrading to WebKit 612.1 (https://bugs.openjdk.java.net/browse/JDK-8268849), webkit fails to compile using XCode 12.5 on Apple Silicone architecture (see below).
Compiling with XCode 12.4 succeeds.

```
In file included from /Users/m1/jenkins/workspace/OpenJFX11u-build-mac-aarch64/modules/javafx.web/src/main/native/Source/WebCore/page/WebKitNamespace.cpp:26:
In file included from /Users/m1/jenkins/workspace/OpenJFX11u-build-mac-aarch64/modules/javafx.web/src/main/native/Source/WebCore/config.h:56:
In file included from /Users/m1/jenkins/workspace/OpenJFX11u-build-mac-aarch64/modules/javafx.web/build/mac/Release/DerivedSources/ForwardingHeaders/wtf/FastMalloc.h:23:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.3.sdk/usr/include/c++/v1/new:90:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.3.sdk/usr/include/c++/v1/exception:80:
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.3.sdk/usr/include/c++/v1/cstddef:49:9: error: no member named 'ptrdiff_t' in the global namespace
using ::ptrdiff_t;
```