When setting up tm.h, convert "vax/vax.h" into "config-vax.h" rather than "[.config.vax]vax.h" for #include so it will work from [.cp] subdirectory...

When setting up tm.h, convert "vax/vax.h" into "config-vax.h" rather
than "[.config.vax]vax.h" for #include so it will work from [.cp]
subdirectory; copy vax.h to config-vax.h as part of configuration
setup.  Also, manually include cc1plus in the list of buildable
compilers (a temporary measure; it should process cp/Makefile.in like
it does for primary makefile).

From-SVN: r7711