spirv: Don't fail if multiple ordering semantics bits are set

spirv: Don't fail if multiple ordering semantics bits are set

Vulkan requires that only one bit for the ordering is set, but old
versions of GLSLang just set all the bits.  This was fixed as part of
https://github.com/KhronosGroup/glslang/commit/c51287d744fb6e7e9ccc09f6f8451e6c64b1dad6
but we can still find older versions (or shaders compiled with it)
around.

So instead of failing, emit a warning and fallback to the effective
result of any combination of multiple bits: AcquireRelease.

Closes: https://gitlab.freedesktop.org/mesa/mesa/issues/2018
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>