Certain programs like dtlogin and tt_type_comp need access to the
system's cpp command to process certain files at runtime. tradcpp is
not installed on most systems, and is intended for use as a imake-cpp
replacement which is all we are using it for. We still need an
honest cpp for the CDE components to use.
Now, we look in various places for a 'cpp' command and set CPP_COMMAND
to it's value. This way tt_type_comp and other CDE programs can do
required processing at runtime.
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