[libspirv] use generic isfinite/isinf/isnan for NVPTX (#22413)
Motivation is to delete include/libspirv/relational.h.
Delete wrong implementation nvptx/relational/clc_isinf.cl, which returns
1 for true in vector input,
while the generic clc_isinf.cl is conforming to OpenCL spec.
Generic implementations are better for nvptx:
- IsFinite: fully vectorized; elimiates fpext and __nv_isfinited calls.
- IsInf: fully vectorized; eliminates __nv_isinf calls.
- IsNan: fully vectorized; elimiates __nv_isnan calls.
