[LLVM][test][nfc] Updating test to work with internal shell

[connieyzhu]

The RUN line attempts to set the JITDUMPDIR environment variable, which fails in llvm-lit's internal shell. This patch prefixes JITDUMPDIR with env so that the behavior of setting the variable is as expected in the internal shell.

Fixes #102395

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[connieyzhu]

cc: @ilovepi @petrhosek

[ilovepi]

LGTM. I'll land this after premerge checks pass.

[ilovepi]

Actually can we change the commit title to something like “Update test to work with internal shell”?

The current title isn’t all that informative IMO.

You should be able to do that with just the edit button above.

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