[SYCL][ABI-Break] Hide some exported symbols

[AlexeySachkov]

Both get_pi_error and set_pi_error are only called from the library and therefore there is no need for them to be exported.

This patch is essentially a by-product of #14145 and it is done to simplify that change, i.e. PI plugins removal should not be ABI-breaking by itself, we just need to cleanup some of our exported symbols.

[AlexeySachkov]

Since the whole intent of this PR is to minimize amount of changes in "drop PI" PR, I'm postponing this rewrite to reduce amount of conflicts.

[aelovikov-intel]

We might not have interop implementing this, but it's theoretically possible. I wonder if that would/might result in an unresolved symbol later on. I'd feel a bit better if we moved it exception.cpp->exception.hpp and made it inline.

WDYT?

[AlexeySachkov]

We might not have interop implementing this, but it's theoretically possible. I wonder if that would/might result in an unresolved symbol later on. I'd feel a bit better if we moved it exception.cpp->exception.hpp and made it inline.

WDYT?

I see that such interop API even documented by the SYCL 2020 spec in C.7.4. Errors and limitations: cl_int sycl::opencl::get_error_code(sycl::exception&) so I agree that the function itself can get more uses. And who knows if the interface would be generalized so it is a templated one which is easier to implement in headers.

No objections against moving the implementation into the header, it is really small

[AlexeySachkov]

We might not have interop implementing this, but it's theoretically possible. I wonder if that would/might result in an unresolved symbol later on. I'd feel a bit better if we moved it exception.cpp->exception.hpp and made it inline.

WDYT?

Applied this comment in e606769