[SYCL] Enable standard optimization pipeline for device code

[bader]

Add new compiler flag to disable optimizations at compile time:
-fno-sycl-std-optimizations

Temporally disable optimizations in some LIT tests.

[bader]

/summary:run

[bader]

/summary:run

[bader]

/summary:run

[bader]

I'd like to commit this patch ASAP to avoid regressions in the future.
There are still a few issues with enabling standard optimization pipeline for SPIR target, but I'll handle them post-commit.
I'm going to introduce a new compiler flag to rollback to old behavior when needed (e.g. -fno-sycl-optimizations).

Let me now if you have any concerns about that plan.

[mdtoguchi]

LGTM

[elizabethandrews]

LGTM except for one question - Should a comment be added to the 2 tests where optimizations were enabled before and now disabled, since this is a temporary change?

[bader]

LGTM except for one question - Should a comment be added to the 2 tests where optimizations were enabled before and now disabled, since this is a temporary change?

I'll open an issue to update all the tests where optimizations were disabled due to different issues (there are more than 2 tests) and add a comment with issue ID to all the tests.