[libclc] [libclc] fix clspv/shared/vstore_half.cl (PR #171105)

[Romaric Jodin via cfe-commits]

rjodinchr wrote:

I found that issue building libclc in Google infra, where the build system is not CMake.

I am not able to reproduce locally with CMake. It seems that the compiler is able to find a system header with the `as_type` functions (without the `__clc_` prefix) 

@wenju-he could you please review ?
Thank you

https://github.com/llvm/llvm-project/pull/171105