[Python-Dev] Proper place to put extra args for building

[Brett C.]

I am currently adding some code for a Py_COMPILER_DEBUG build for use on the
AST branch.  I thought that OPT was the proper variable to put stuff like this
into for building (``-DPy_COMPILER_DEBUG``), but that erases ``-g -Wall
-Wstrict-prototypes``.  Obviously I could just tack all of that into my own
thing, but that seems like an unneeded step.

>From looking at Makefile.pre.in it seems like CFLAGSFORSHARED is meant for
extra arguments to the compiler.  Is that right?

And I will document this in Misc/Specialbuilds.txt to fix my initial blunderous
checkin of specifying OPT (or at least clarifying it).

-Brett