watchOS builds fail with ASan enabled.

```
In file included from DerivedSources/JavaScriptCore/unified-sources/UnifiedSource7.cpp:1:
In file included from ./assembler/MacroAssemblerPrinter.cpp:27:
In file included from ./assembler/MacroAssemblerPrinter.h:31:
In file included from ./assembler/ProbeContext.h:29:
./assembler/ProbeStack.h:139:5: error: static assertion failed due to requirement 's_chunkSize == (1 << s_chunkSizeShift)': bad chunkSizeShift
    static_assert(s_chunkSize == (1 << s_chunkSizeShift), "bad chunkSizeShift");
    ^             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./assembler/ProbeStack.h:139:31: note: expression evaluates to '4 == 8'
    static_assert(s_chunkSize == (1 << s_chunkSizeShift), "bad chunkSizeShift");
                  ~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.
```