[llvm] [BOLT][test] Allow uninstantiated tests when no matching targets are enabled (PR #217604)

[Rong Mantle Bao via llvm-commits]

CSharperMantle wrote:

> Is it possible to instantiate the tests for RISC-V or do they cause failures?

RISCV currently doesn't have corresponding tests implemented, so without this declaration the testbench would fail to run.

See also PointerAuthCFIFixup.cpp, which is also a arch-specific test case.

https://github.com/llvm/llvm-project/blob/a26d1318959d4d06f0881a8d6041e9fc551cd175/bolt/unittests/Passes/PointerAuthCFIFixup.cpp#L125

https://github.com/llvm/llvm-project/pull/217604