message: Adjust License.txt file to use the LLVM license
diff: -Copyright 2019 The MLIR Authors.
  +==============================================================================
  +The LLVM Project is under the Apache License v2.0 with LLVM Exceptions:
  +==============================================================================
  Apache License
  Version 2.0, January 2004
  @@ -203,3 +205,75 @@ Copyright 2019 The MLIR Authors.
  limitations under the License.
  +---- LLVM Exceptions to the Apache 2.0 License ----
  +
  +As an exception, if, as a result of your compiling your source code, portions
  +of this Software are embedded into an Object form of such source code, you
  +may redistribute such embedded portions in such Object form without complying
  +with the conditions of Sections 4(a), 4(b) and 4(d) of the License.
  +
  +In addition, if you combine or link compiled forms of this Software with
  +software that is licensed under the GPLv2 ("Combined Software") and if a
  +court of competent jurisdiction determines that the patent provision (Section
  +3), the indemnity provision (Section 9) or other Section of the License
  +conflicts with the conditions of the GPLv2, you may retroactively and
  +prospectively choose to deem waived or otherwise exclude such Section(s) of
  +the License, but only in their entirety and only with respect to the Combined
  +Software.
  +
  +==============================================================================
  +Software from third parties included in the LLVM Project:
  +==============================================================================
  +The LLVM Project contains third party software which is under different license
  +terms. All such code will be identified clearly using at least one of two
  +mechanisms:
  +1) It will be in a separate directory tree with its own `LICENSE.txt` or
  + `LICENSE` file at the top containing the specific license and restrictions
  + which apply to that software, or
  +2) It will contain specific license and restriction terms at the top of every
  + file.
  +
  +==============================================================================
  +Legacy LLVM License (https://llvm.org/docs/DeveloperPolicy.html#legacy):
  +==============================================================================
  +University of Illinois/NCSA
  +Open Source License
  +
  +Copyright (c) 2003-2019 University of Illinois at Urbana-Champaign.
  +All rights reserved.
  +
  +Developed by:
  +
  + LLVM Team
  +
  + University of Illinois at Urbana-Champaign
  +
  + http://llvm.org
  +
  +Permission is hereby granted, free of charge, to any person obtaining a copy of
  +this software and associated documentation files (the "Software"), to deal with
  +the Software without restriction, including without limitation the rights to
  +use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
  +of the Software, and to permit persons to whom the Software is furnished to do
  +so, subject to the following conditions:
  +
  + * Redistributions of source code must retain the above copyright notice,
  + this list of conditions and the following disclaimers.
  +
  + * Redistributions in binary form must reproduce the above copyright notice,
  + this list of conditions and the following disclaimers in the
  + documentation and/or other materials provided with the distribution.
  +
  + * Neither the names of the LLVM Team, University of Illinois at
  + Urbana-Champaign, nor the names of its contributors may be used to
  + endorse or promote products derived from this Software without specific
  + prior written permission.
  +
  +THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  +IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
  +FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  +CONTRIBUTORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  +LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  +OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS WITH THE
  +SOFTWARE.
  +
  