[REG: 6.9 -> 6.10] Invalid syntax generated in WebEngine pch and ccache build after recent change

This happened on macOS Sononma 14.6.1, XCode 16, Apple clang version 16.0.0 (clang-1600.0.26.6), Target: arm64-apple-darwin23.6.0.

When building Qt WebEngine with current dev qtbase (51c7503568174669b48a8f8ddbe49eebb127a128) using ccache and precompiled headers, the ninja file seems to contain invalid syntax, which causes the build to fail. I think this is a result of this change: https://codereview.qt-project.org/c/qt/qtbase/+/637926

The build fails with:

 [...] SHELL:-Xclang\ -fno-pch-timestamp -ftrivial-auto-var-init=pattern -fstack-protector-strong -fno-exceptions -x c++-header -c ../../../../../../../../../Users/michaelbruning/qt-src/dev/qtwebengine/src/3rdparty/chromium/build/precompile.h -o obj/QtWebEngineCore/precompile.h-cc.gch
clang++: error: unknown argument '-fno-pch-timestamp'; did you mean '-Xclang -fno-pch-timestamp'?
clang++: error: no such file or directory: 'SHELL:-Xclang'
clang++: error: no such file or directory: 'SHELL:-Xclang -fno-pch-timestamp'
[...]

FAILED: src/core/Release/arm64/QtWebEngineCore.stamp

(full line of the failure from the log attached).

The cflags and cflags_cc sections in the attached QTWebEngineCore.ninja file contain the following flag:

SHELL$:-Xclang -fno-pch-timestamp

QtBase configure options: -ccache -framework -release -force-debug-info -separate-debug-info -nomake examples -nomake tests -no-openssl -shared -securetransport -prefix /Users/michaelbruning/install/dev – -DCMAKE_OSX_ARCHITECTURES=arm64

QtWebEngine configure module options: -webengine-proprietary-codecs -webengine-full-debug-info – -DQT_BUILD_TESTS=ON -DQT_BUILD_EXAMPLES=ON

CMake version: 3.23.3