[CIR][NEON] Add lowering support for `vceqzd_s64` (#179779)
Rather than creating a dedicated ClangIR test file, the original test file for
this intrinsic is effectively reused:
* clang/test/CodeGen/AArch64/neon-intrinsics.c
“Effectively” meaning that the corresponding test is moved (rather than
literally reused) to a new file within the original AArch64 builtins test
directory:
* clang/test/CodeGen/AArch64/neon/intrinsics.c
This is necessary to avoid lowering unsupported examples from intrinsics.c with
`-fclangir`. The new file will eventually replace the original one once all
builtins from it can be lowered via ClangIR.
To facilitate test re-use, new LIT "feature" is added so that CIR tests can be
run conditionally, e.g. the following will only run when `CLANG_ENABLE_CIR` is
set:
```C
// RUN: %if cir %{%clang_cc1 ... %}
```
This sort of substitutions are documented in [2].
REFERENCES:
[1] https://developer.arm.com/architectures/instruction-sets/intrinsics/#f:@navigationhierarchiessimdisa=[Neon]&q=vceqzd_s64
[2] https://llvm.org/docs/TestingGuide.html#substitutions
llvm-project
80677dc5 - [CIR][NEON] Add lowering support for `vceqzd_s64` (#179779)
