liblzma: Add .gitattributes to ignore whitespace checks

Tell Git not to check whitespace in third-party code.
liblzma 5.0.5-gb69900ed (reduced)

Extract upstream liblzma using the following shell code.

url=http://git.tukaani.org/xz.git &&
v=5.0.5 &&
r=b69900ed &&
paths="
  COPYING
  src/common/common_w32res.rc
  src/common/sysdefs.h
  src/common/tuklib_integer.h
  src/liblzma
" &&
mkdir liblzma-$v-g$r-reduced &&
git clone $url liblzma-git &&
date=$(cd liblzma-git && git log -n 1 --format='%cd' $r) &&
(cd liblzma-git && git archive --format=tar $r -- $paths) |
(cd liblzma-$v-g$r-reduced && tar xv &&
 mv src/* . && rmdir src) &&
echo "g$r date: $date"
Merge branch 'liblzma-upstream' into add-liblzma
liblzma: Add README-CMake.txt

Describe how to update liblzma from upstream.
liblzma: Remove unused Makefile.* files

We will provide our own CMake-based build system.
liblzma: Add CMake build system

Modify sources just enough to build without the full xz common
directory.
liblzma: Port from C99 to C89/90
liblzma: Port to VS 6
CMake: Enable use of liblzma in libarchive (#14504)

Build liblzma as part of CMake or find one on the system.  Modify our
port of libarchive to use the liblzma configured for use with CMake.
Merge topic 'add-liblzma' into next

2e45b40f CMake: Enable use of liblzma in libarchive (#14504)
7ee85157 liblzma: Port to VS 6
0430e5dd liblzma: Port from C99 to C89/90
b2a07ca4 liblzma: Add CMake build system
d44ad161 liblzma: Remove unused Makefile.* files
a53caea3 liblzma: Add README-CMake.txt
133d42fe Merge branch 'liblzma-upstream' into add-liblzma
c289e634 liblzma 5.0.5-gb69900ed (reduced)
8510533f liblzma: Add .gitattributes to ignore whitespace checks