[clang] [clang][Sema] Allow splat initialization of a sizeless vector in a C++ code (PR #205432)

[Jonathan Thackray via cfe-commits]

jthackray wrote:

Ok, so it look like this crashes during codegen:
```
typedef __SVBool_t svbool_t;

void sink(svbool_t);

void f(int i) {
  sink(i);
}
```
when `-emit-llvm` gives:
```
% rel/bin/clang -cc1 -triple aarch64 -target-feature +sve -emit-llvm -o - crash.cpp
clang: /home/jontha01/llvm-project/clang/lib/CodeGen/CGCall.cpp:5898: RValue clang::CodeGen::CodeGenFunction::EmitCall(const CGFunctionInfo &, const CGCallee &, ReturnValueSlot, const CallArgList &, llvm::CallBase **, bool, SourceLocation, bool): Assertion `V->getType()->isPointerTy() && "Only pointers can mismatch!"' failed.
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace and dumped files.
Stack dump:
0.	Program arguments: rel/bin/clang -cc1 -triple aarch64 -target-feature +sve -std=c++17 -emit-llvm -o - crash.cpp
1.	<eof> parser at end of file
2.	crash.cpp:5:6: LLVM IR generation of declaration 'f'
3.	crash.cpp:5:6: Generating code for declaration 'f'
```

https://github.com/llvm/llvm-project/pull/205432