AUTOMOC used to fail to generate ``moc_predefs.h`` when ``ccache`` was used
as a compiler starter by e.g. configuring a project with the environment
variable CXX="ccache g++".
The reason was that ``CMAKE_<LANG>_COMPILER_ARG1`` wasn't respected in the
definition of ``CMAKE_<LANG>_COMPILER_PREDEFINES_COMMAND`` for various
compilers.  This is fixed by this patch.

Fixes #17275.