This is to fix buildbot failure
https://lab.llvm.org/staging/#/builders/195/builds/4255.
The test expects 'libstdc++' or 'libc++' SO module in the module list.
In case when static linking with libc++ is on by default, none of them
may be present.
Thus, USE_SYSTEM_STDLIB is added to ensure the presence of any of them.
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Co-authored-by: Vladimir Vereschaka <vvereschaka@accesssoftek.com>
f035d9f061