[compiler-rt][UBSan] Add env prefixes in test

This was another test that was not using an env prefix when setting an
environment variable. This was caught by the Sparc Solaris builder as it
is disabled by default on Linux.

https://lab.llvm.org/buildbot/#/builders/13/builds/10414

GitOrigin-RevId: d46ed73de883ea6013e0727b4b91ee06dac14b4f
1 file changed