[DirectX] Unable to use global resource handles with `-O0`

[Icohedron]

With -O0, global resource handles can not be used due to error error: Load of "" is not a global resource handle.

// RUN: clang-dxc -E CSMain -T cs_6_7 -O0 %s
RWBuffer<uint> output : register(u0);
[numthreads(1,1,1)]
void CSMain() { 
    output[0] = 0;
}

Reproduction: https://godbolt.org/z/6vP5xxYsE

[llvmbot]

@llvm/issue-subscribers-bug

Author: Deric C. (Icohedron)

With `-O0`, global resource handles can not be used due to error `error: Load of "" is not a global resource handle`.

// RUN: clang-dxc -E CSMain -T cs_6_7 -O0 %s
RWBuffer<uint> output : register(u0);
[numthreads(1,1,1)]
void CSMain() { 
    output[0] = 0;
}

Reproduction: https://godbolt.org/z/6vP5xxYsE