[llvm] [SLP] Better way to filter target-specific tests (PR #106720)

[Elvina Yakubova via llvm-commits]

ElvinaYakubova wrote:

When only an exclusive target e.g AArch64 was enabled, these tests were previously shown as UNSUPPORTED.
This change allows us to run tests for cases where we only have a build for one target.

https://github.com/llvm/llvm-project/pull/106720