[Distutils] msvccompiler clobbers LIB/INCLUDE vars

[Mark Hammond]

I've recently noticed that msvccompiler clobbers the LIB and INCLUDE
environment variables set in the environment.  What happens is that
distutils looks up the registry entries for the DevStudio include and lib
file settings, then *sets* the LIB and INCLUDE environment with these
values, ignoring any previous values.

It is quite common (for me anyway <wink>) to say something like:
set LIB=%LIB%;c:\some_obscure_sdk\lib
set INCLUDE=%INCLUDE%;c:\some_obscure_sdk\include
make

But if I try and use the same technique with distutils, these variable
values are lost.

It seems the *only* way I can add new paths that will work with distutils is
via the DevStudio GUI, rather than these standard environment variables.  Is
that the intent?  I understand we need to work when these variables are not
set.

Thanks,

Mark.