C++ for OpenCL: Unresolved external reference to _Z13get_global_idj

The translator is generating spirv with function calls which should be treated as builtins.

This is only occurring when clang is run with the C++ for OpenCL mode.

When run in `clc++` mode, clang generates a `!opencl.cxx.version = !{!3}` entry, which seems to be causing some issues.

Here is an easy way to reproduce:

kernel.cl:
```C
// this sample doesn't use any C++ for OpenCL features
__kernel void sample(write_only image2d_t img) {

const int col = get_global_id(0);
const int row = get_global_id(1);
int2 coord;
coord.x = col;
coord.y = row;

float4 px = {0, 0, 0, 1};

write_imagef(img, coord, px);
}
```
run:
`clang -target spirv64 -cl-std=clc++ kernel.cl`
`error: 0: Unresolved external reference to "_Z13get_global_idj".`

Examine the generated spirv:
`clang -c -target spirv64 -cl-std=clc++ -emit-llvm -o - kernel.cl | llvm-spirv -o - | spirv-dis`
Notice how the spirv contains some odd `OpFunctionCall`:
```
%22 = OpFunctionCall %ulong %_Z13get_global_idj %uint_0
%23 = OpUConvert %uint %22
%25 = OpFunctionCall %ulong %_Z13get_global_idj %uint_1
%26 = OpUConvert %uint %25
%28 = OpCompositeInsert %v2uint %23 %27 0
%29 = OpCompositeInsert %v2uint %26 %28 1
%33 = OpFunctionCall %void %_Z12write_imagef14ocl_image2d_woDv2_iDv4_f %19 %29 %32
```

Looking at the llvm generated by clang:
`clang -c -target spirv64 -cl-std=clc++ -emit-llvm -o - kernel.cl | llvm-dis`
Notice the `!opencl.cxx.version = !{!3}`

If I edit the llvm, and pass it back through llvm-spirv:
```
clang -c -target spirv64 -cl-std=clc++ -emit-llvm -o - kernel.cl \
| llvm-dis -o - \
| sed '/!opencl.cxx.version/d' \
| llvm-as -o - \
| llvm-spirv -o - \
| spirv-dis
```
The output appears normal:
```
%12 = OpLoad %v3ulong %__spirv_BuiltInGlobalInvocationId Aligned 32
%13 = OpCompositeExtract %ulong %12 0
%15 = OpUConvert %uint %13
%16 = OpLoad %v3ulong %__spirv_BuiltInGlobalInvocationId Aligned 32
%17 = OpCompositeExtract %ulong %16 1
%18 = OpUConvert %uint %17
%21 = OpCompositeInsert %v2uint %15 %20 0
%22 = OpCompositeInsert %v2uint %18 %21 1
OpImageWrite %10 %22 %27
```

We can verify that this links correctly by running `spirv-link`.

Repeating the same processes, but running clang without `-cl-std=clc++` results in no errors. The only meaningful difference in the generated llvm is the `!opencl.cxx.version = !{!3}` tag

related issue: https://github.com/llvm/llvm-project/issues/118576

Start by reproducing the issue with the provided clang -cl-std=clc++ pipeline, then inspect how the !opencl.cxx.version metadata is handled by llvm-spirv. Compare the generated SPIR-V with and without that metadata; done means get_global_id and write_imagef are emitted as builtins and the result links successfully with spirv-link.

Written by the indexing model from the issue text.