Merging r296358 and r296359:

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r296358 | aadg | 2017-02-27 09:33:20 -0800 (Mon, 27 Feb 2017) | 8 lines

Add libcxxabi's LICENSE.TXT to libunwind.

When libunwind was spinned off libcxxabi, most file were copied from
libcxxabi to libunwind.  However, libc++abi's toplevel LICENSE.TXT was
forgotten in the copying. It's considered a good practice to have the
license file at the root of the project, and making linunwind a separate
project was not supposed to change its licensing. Besides, several
header files refer to the LICENSE.TXT, so copy the one from libc++abi.
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r296359 | aadg | 2017-02-27 09:47:58 -0800 (Mon, 27 Feb 2017) | 1 line

Fix the project name in the license file.
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llvm-svn: 296364