[DeveloperPolicy] Specify LLVM's license more clearly.

[kristof.beyls]

Summary

Before, the first mention of LLVM's license on the developer policy page stated
that LLVM's license is Apache 2. This patch makes that more accurate by
mentioning the LLVM exception this first time the LLVM license is discussed on
that page, i.e. Apache-2.0 with LLVM-exception.

Technically, the correct SPDX identifier for LLVM's license is 'Apache-2.0 WITH
LLVM-exception', but I thought that writing the 'WITH' in lower case made the
paragraph easier to read without reducing clarity.

[tschuett]

If you would extend the paragraph, you could say:
"For reference the SPDX identifier is ..."

[kristof.beyls]

In D96482#2556315, @tschuett wrote:

If you would extend the paragraph, you could say:
"For reference the SPDX identifier is ..."

Yes, it could be helpful to also explicitly call out the SPDX identifier. However, there is also value in keeping that introductory paragraph as short as possible.
On balance, I think it's slightly better to not call out the SPDX identifier in that introductory paragraph.
Maybe there's value in explicitly calling out the SPDX identifiers in one of the later paragraphs?

[tschuett]

In D96482#2556325, @kristof.beyls wrote:

In D96482#2556315, @tschuett wrote:

If you would extend the paragraph, you could say:
"For reference the SPDX identifier is ..."

Yes, it could be helpful to also explicitly call out the SPDX identifier. However, there is also value in keeping that introductory paragraph as short as possible.
On balance, I think it's slightly better to not call out the SPDX identifier in that introductory paragraph.
Maybe there's value in explicitly calling out the SPDX identifiers in one of the later paragraphs?

Agreed. In fact, I could neither find a WITH nor a SPDX in the whole file.

[tschuett]

There is also no LLVM-exception with a dash.

[lattner]

Looks great, thank you!

llvm/docs/DeveloperPolicy.rst

 .. note::
 
    This section deals with legal matters but does not provide legal advice.  We
    are not lawyers --- please seek legal counsel from a licensed attorney.
 
 This section addresses the issues of copyright, license and patents for the LLVM
 project.  The copyright for the code is held by the contributors of
 the code.  The code is licensed under permissive `open source licensing terms`_,
-namely the Apache 2 license, which includes a copyright and `patent license`_.
-When you contribute code to the LLVM project, you license it under these terms.
+namely the Apache-2.0 with LLVM-exception license, which includes a copyright
+and `patent license`_.  When you contribute code to the LLVM project, you
+license it under these terms.
 
 If you have questions or comments about these topics, please contact the
 `LLVM Developer's Mailing List <mailto:[e-mail]>`_.  However,
 please realize that most compiler developers are not lawyers, and therefore you
 will not be getting official legal advice.
 
 Copyright
 ---------