customcc/compilers.conf: Some adjustments and simplifications.

customcc/compilers.conf: Some adjustments and simplifications.

* pkgsrc's clang no longer needs special handling for C++ compilation.

* Use gcc44's cpp, gcc41 is gone.

* -dumpversion is now understool by both pkgsrc's and SVN trunk's
  clang, so no special handling needed for that either.

Based on an older patch I did with Juan Francisco a year ago.

Reported-by:   Juan Francisco Cantero Hurtado <iam@juanfra.info>
               Joris Giovannangeli <joris@giovannangeli.fr>
Tested-by:     Joris Giovannangeli <joris@giovannangeli.fr>
Dragonfly-bug: <http://bugs.dragonflybsd.org/issues/2205>