WebKit_iosmac builds fail with ASan enabled.

This occurs because iosmac builds with ASan enabled have ENABLE(IPC_TESTING_API) turned on and ENABLE(ENCRYPTED_MEDIA)/ENABLE(LEGACY_ENCRYPTED_MEDIA) turned off.

'''
BuiltProducts/DerivedSources/WebKit/MessageArgumentDescriptions.cpp:9050:54: error: no member named 'RemoteCDMIdentifier' in namespace 'WebKit'
    static_assert(sizeof(uint64_t) == sizeof(WebKit::RemoteCDMIdentifier));
                                             ~~~~~~~~^
BuiltProducts/DerivedSources/WebKit/MessageArgumentDescriptions.cpp:9051:54: error: no member named 'RemoteCDMInstanceIdentifier' in namespace 'WebKit'
    static_assert(sizeof(uint64_t) == sizeof(WebKit::RemoteCDMInstanceIdentifier));
                                             ~~~~~~~~^
BuiltProducts/DerivedSources/WebKit/MessageArgumentDescriptions.cpp:9052:54: error: no member named 'RemoteCDMInstanceSessionIdentifier' in namespace 'WebKit'
    static_assert(sizeof(uint64_t) == sizeof(WebKit::RemoteCDMInstanceSessionIdentifier));
                                             ~~~~~~~~^
BuiltProducts/DerivedSources/WebKit/MessageArgumentDescriptions.cpp:9053:54: error: no member named 'RemoteLegacyCDMIdentifier' in namespace 'WebKit'
    static_assert(sizeof(uint64_t) == sizeof(WebKit::RemoteLegacyCDMIdentifier));
                                             ~~~~~~~~^
BuiltProducts/DerivedSources/WebKit/MessageArgumentDescriptions.cpp:9054:54: error: no member named 'RemoteLegacyCDMSessionIdentifier' in namespace 'WebKit'
    static_assert(sizeof(uint64_t) == sizeof(WebKit::RemoteLegacyCDMSessionIdentifier));
                                             ~~~~~~~~^
5 errors generated.
'''

<rdar://105597825>