Bump LLVM to 13.0.0 for android builds

context

we want to use LLVM version 13.0.0 for android builds (as it is the latest version and is what mozilla uses upstream for geckoview)
however: we are unable to build geckoview v96.0.x if we do so, b/c clang_rt errors, as per: !405 (comment 2776669)
for the purposes of !406 (merged) , we reverted to 12.0.0 for nightly, but want to resolve 13.0.0 before tagging next alpha release (11.5a5)

changes

use llvm v13.0.0 (with git_hash: d7b669b3a30345cfcdb2fde2af6f48aa4b94845d) in projects/llvm-project/config.targets.android

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