Fix typos in comments.
xz: Fix use of wrong variable.

Since the only call to suffix_set() uses optarg
as the argument, fixing this bug doesn't change
the behavior of the program.
liblzma: Remove a useless C99ism from sha256.c.

Unsurprisingly it makes no difference in compiled output.
liblzma: Avoid C99 compound literal arrays.

MSVC 2013 doesn't like them. Maybe they aren't so good
for readability either since many aren't used to them.
Windows: Add MSVC defines for inline and restrict keywords.
xz: Fix a comment.
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.
liblzma: Fix typo in a comment.