[llvm-exgesis][NFC] Do not pollute buildbots with messages when the exegesis lit tests cannot run.
[llvm-exgesis][NFC] Do not pollute buildbots with messages when
the exegesis lit tests cannot run.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@343110 91177308-0d34-0410-b5e6-96231b3b80d8

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