Log Message:
greatly simplify the handling of pkgsrc gcc, and eliminate a bug which
has allowed these packages to work :)

set CC, CXX, CPP and F77 in gcc{,3}/buildlink2.mk.

you now only need to define USE_GCC2 or USE_GCC3 to use the pkgsrc
gcc of your choice.

the share/examples/gcc/mk.conf and gcc3/mk.conf files are no longer
installed.

bump PKGREVISIONs.