Add GitHub source for org_lzma_lzma http_archive.

The Fedora URL is sometimes flaky and causes download errors when fetching the dependency for boost.

Example errors:

google/xls#3254

```
ERROR: /home/testing/.cache/bazel/_bazel_testing/5eeddc84bceff4fbe76fd8c516cb1790/external/bazel_tools/tools/build_defs/repo/http.bzl:136:45: An error occurred during the fetch of repository 'org_lzma_lzma':
   Traceback (most recent call last):
	File "/home/testing/.cache/bazel/_bazel_testing/5eeddc84bceff4fbe76fd8c516cb1790/external/bazel_tools/tools/build_defs/repo/http.bzl", line 136, column 45, in _http_archive_impl
		download_info = ctx.download_and_extract(
Error in download_and_extract: java.io.IOException: Error downloading [https://src.fedoraproject.org/lookaside/extras/xz/xz-5.4.6.tar.gz/sha512/b08a61d8d478d3b4675cb1ddacdbbd98dc6941a55bcdd81a28679e54e9367d3a595fa123ac97874a17da571c1b712e2a3e901c2737099a9d268616a1ba3de497/xz-5.4.6.tar.gz] to /home/testing/.cache/bazel/_bazel_testing/5eeddc84bceff4fbe76fd8c516cb1790/external/org_lzma_lzma/temp214682858572773859/xz-5.4.6.tar.gz: Connect timed out
```

Author: mikex-oss

dependency_support/boost/downgrade_lzma.patch

@@ -2,16 +2,19 @@ diff --git boost/boost.bzl boost/boost.bzl
 index 4381996..587a37d 100644
 --- boost/boost.bzl
 +++ boost/boost.bzl
-@@ -140,9 +140,9 @@ def boost_deps():
+@@ -140,9 +140,12 @@ def boost_deps():
          http_archive,
          name = "org_lzma_lzma",
          build_file = "@com_github_nelhage_rules_boost//:lzma.BUILD",
 -        url = "https://github.com/tukaani-project/xz/releases/download/v5.4.3/xz-5.4.3.tar.gz",
 -        sha256 = "1c382e0bc2e4e0af58398a903dd62fff7e510171d2de47a1ebe06d1528e9b7e9",
 -        strip_prefix = "xz-5.4.3",
-+        url = "https://src.fedoraproject.org/lookaside/extras/xz/xz-5.4.6.tar.gz/sha512/b08a61d8d478d3b4675cb1ddacdbbd98dc6941a55bcdd81a28679e54e9367d3a595fa123ac97874a17da571c1b712e2a3e901c2737099a9d268616a1ba3de497/xz-5.4.6.tar.gz",
++        urls = [
++            "https://github.com/tukaani-project/xz/releases/download/v5.4.6/xz-5.4.6.tar.gz",
++            "https://src.fedoraproject.org/lookaside/extras/xz/xz-5.4.6.tar.gz/sha512/b08a61d8d478d3b4675cb1ddacdbbd98dc6941a55bcdd81a28679e54e9367d3a595fa123ac97874a17da571c1b712e2a3e901c2737099a9d268616a1ba3de497/xz-5.4.6.tar.gz",
++        ],
 +        sha256 = "aeba3e03bf8140ddedf62a0a367158340520f6b384f75ca6045ccc6c0d43fd5c",
 +        strip_prefix = "xz-5.4.6",
      )
- 
+
      maybe(