Windows: Add config.h for building liblzma with MSVC 2013.

This is for building liblzma. Building xz tool too requires
a little more work. Maybe it will be supported, but for most
MSVC users it's enough to be able to build liblzma.

C99 support in MSVC 2013 is almost usable which is a big
improvement over earlier versions. It's "almost" because
there's a dumb bug that breaks mixed declarations after
an "if" statements unless the "if" statement uses braces:

https://connect.microsoft.com/VisualStudio/feedback/details/808650/visual-studio-2013-c99-compiler-bug
https://connect.microsoft.com/VisualStudio/feedback/details/808472/c99-support-of-mixed-declarations-and-statements-fails-with-certain-types-and-constructs

Hopefully it will get fixed. Then liblzma should be
compilable with MSVC 2013 without patching.
1 file changed