Revert "Remove unused language pragma"
Revert "Remove unused language pragma"

This reverts commit 7d1909ad110f05c8cb2fb0689ee75857ceb945f6.

It is actually used for Callstacks, woops!

ezyang/ghc,shlevy/ghc,sdiehl/ghc,shlevy/ghc,ezyang/ghc,sdiehl/ghc,ezyang/ghc,sdiehl/ghc,shlevy/ghc,ezyang/ghc,sdiehl/ghc,shlevy/ghc,shlevy/ghc,ezyang/ghc,sdiehl/ghc,ezyang/ghc,shlevy/ghc,ezyang/ghc,shlevy/ghc,sdiehl/ghc,sdiehl/ghc