[SYCL][Fusion] Pass -O2 flag to tests performing argument promotion

[victor-eds]

No promotion will take place if -O0 is passed, so add this flag to override options possibly disrupting tests results.

[sommerlukas]

LGTM.

[steffenlarsen]

We recently saw cases where -O flags were ignored on Windows because the test-suite uses clang-cl. As such I worry this only avoid the problem on Linux. A more stable solution could be to introduce new LIT variables picking -O2 or /O2 depending on the target.

[sommerlukas]

We recently saw cases where -O flags were ignored on Windows because the test-suite uses clang-cl. As such I worry this only avoid the problem on Linux. A more stable solution could be to introduce new LIT variables picking -O2 or /O2 depending on the target.

Note that fusion is currently only supported on Linux. On Windows, the LIT configuration feature fusion is not available, so all the tests with the -O flag should be marked unsupported by the REQUIRES: fusion clause.

[steffenlarsen]

Note that fusion is currently only supported on Linux. On Windows, the LIT configuration feature fusion is not available, so all the tests with the -O flag should be marked unsupported by the REQUIRES: fusion clause.

Point taken! In that case, I am okay with this. If Windows support is added in the future, please keep my previous comment in mind. 😄