Make "make clean" rules a bit more standard.

Make "make clean" rules a bit more standard.

Summary:
make-generic is some sort of internal undocumented thing.
make-local is what is supposed to be used for this stuff.
Also use $(RM) instead of "rm -f".

Reviewed By: marc

Test Plan: make clean

git-svn-id: https://svn.apache.org/repos/asf/incubator/thrift/trunk@665498 13f79535-47bb-0310-9956-ffa450edef68