Switch the license to Apache 2.0, matching OpenSSL upstream

We use the standard Apache 2.0 file header, described in "APPENDIX: How
to apply the Apache License to your work."

This was primarily automated by running:

  git ls-tree -r --name-only HEAD | xargs go run ./util/relicense.go

See go/boringssl-relicensing-triage for the results of triaging the
output of the tool.

As part of this, switch from taking fiat-crypto under MIT license to
Apache 2.0. (It is licensed under MIT OR Apache-2.0 OR BSD-1-Clause.)

The copyright_summary tool can also be used to confirm we didn't
accidentally drop any copyright lines:

  # Run before the CL
  git grep -l Copyright | xargs go run ./util/copyright_summary.go  -out /tmp/old.json
  # Run after the CL
  git grep -l Copyright | xargs go run ./util/copyright_summary.go  -compare /tmp/old.json

Bug: 364634028
Change-Id: I17c50e761e9d077a1f92e25969e50ed35e320c59
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/75852
Reviewed-by: Bob Beck <bbe@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/third_party/fiat/AUTHORS b/third_party/fiat/AUTHORS
new file mode 100644
index 0000000..b67f8f9
--- /dev/null
+++ b/third_party/fiat/AUTHORS
@@ -0,0 +1,17 @@
+# This is the official list of fiat-crypto authors for copyright purposes.
+# This file is distinct from the CONTRIBUTORS files.
+# See the latter for an explanation.
+
+# Names should be added to this file as one of
+#     Organization's name
+#     Individual's name <submission email address>
+#     Individual's name <submission email address> <email2> <emailN>
+# See CONTRIBUTORS for the meaning of multiple email addresses.
+
+# Please keep the list sorted.
+
+Andres Erbsen <andreser@mit.edu>
+Google Inc.
+Jade Philipoom <jadep@mit.edu> <jade.philipoom@gmail.com>
+Massachusetts Institute of Technology
+Zoe Paraskevopoulou <zoe.paraskevopoulou@gmail.com>
\ No newline at end of file
diff --git a/third_party/fiat/LICENSE b/third_party/fiat/LICENSE
index 70cae03..3bc4b88 100644
--- a/third_party/fiat/LICENSE
+++ b/third_party/fiat/LICENSE
@@ -1,22 +1,15 @@
-The MIT License (MIT)
+The Apache License, Version 2.0 (Apache-2.0)
 
-Copyright (c) 2015-2020 the fiat-crypto authors (see
-https://github.com/mit-plv/fiat-crypto/blob/master/AUTHORS).
+Copyright 2015-2020 the fiat-crypto authors (see the AUTHORS file)
 
-Permission is hereby granted, free of charge, to any person obtaining a copy
-of this software and associated documentation files (the "Software"), to deal
-in 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:
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
 
-The above copyright notice and this permission notice shall be included in all
-copies or substantial portions of the Software.
+    http://www.apache.org/licenses/LICENSE-2.0
 
-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
-AUTHORS 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 IN THE
-SOFTWARE.
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
diff --git a/third_party/fiat/README.chromium b/third_party/fiat/README.chromium
index fdf28a4..b19c040 100644
--- a/third_party/fiat/README.chromium
+++ b/third_party/fiat/README.chromium
@@ -3,7 +3,7 @@
 URL: https://github.com/mit-plv/fiat-crypto
 Version: git (see METADATA)
 Revision: 6ccc6638716d4632304baf1adbb5c47c3a12ea6f
-License: MIT
+License: Apache 2.0
 License File: LICENSE
 Security Critical: yes
 Shipped: yes
diff --git a/third_party/fiat/README.md b/third_party/fiat/README.md
index 9c1fc87..1035e7f 100644
--- a/third_party/fiat/README.md
+++ b/third_party/fiat/README.md
@@ -3,7 +3,7 @@
 The files in this directory are generated using [Fiat
 Cryptography](https://github.com/mit-plv/fiat-crypto) from the associated
 library of arithmetic-implementation templates. These files are included under
-the MIT license. (See LICENSE file.)
+the Apache 2.0 license. (See LICENSE file.)
 
 Some files are included directly from the `fiat-c/src` directory of the Fiat
 Cryptography repository. Their contents are `#include`d into source files, so