[libcxx] [llvm] [libc++] Make CC and CXX environment variables mandatory in run-buildbot (PR #166875)

[Louis Dionne via llvm-commits]

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@@ -96,6 +120,23 @@ function error() {
     echo "::error::$1"
 }
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ldionne wrote:

Good catch, I somehow messed up my diff.

https://github.com/llvm/llvm-project/pull/166875