[Distutils] The role and functionality of customize_compiler

[Poor Yorick]

It looks like the defaults for ccompiler.executables that are set in
compiler-specific sublcasses like UnixCCompiler are always overridden by
customize_compiler in sysconfig.py.  For example, in UnixCcompiler the value
for executables['compiler'] is ["cc"], but this will never be used because
comtomize_compiler invariably grabs the compiler value out of the Python
Makefile and uses that.  Should customize_compiler be reorganized a bit so that
defaults are actually used if customize_compiler comes up empty-handed for
certain values?

Next, it looks like customize_compiler is really a method of UnixCcompiler
disguised as an independent function.  Would it make sense for Ccompiler to
have an abstract method, "customize", and to move the current
customize_compiler function into UnixCcompiler?

On the topic of include directories, would it make sense to add a
"sysinclude_dirs" option to the Extension class in order separate out the two
different uses that include_dirs currently plays in setup.py scripts?

-- 
Yorick