[release-1.2] bazel: replace tclap mirror. (#9072)

[yxue]

Description:

Change (non-existent) https://github.com/eile/tclap/ to https://github.com/mirror/tclap/. I didn't validate the new mirror in any way, but the downloded release file sha256sum stays the same. In the future the releases should probably be downloaded from the real upstream. However the release 1.2.1 tarball from https://sourceforge.net/projects/tclap/files/ did not have the same sha256sum as the release file which Envoy uses.

Risk Level: Medium
Testing: N/A
Docs Changes: N/A
Release Notes:
Fixes envoyproxy#9071

Signed-off-by: Ismo Puustinen ismo.puustinen@intel.com
Signed-off-by: Yan Xue yxyan@google.com

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