[OpenCL] Remove fast_ half geometric builtins

[svenvh]

Summary

These are not mentioned in the OpenCL C Specification nor in the
OpenCL Extension Specification.

[Anastasia]

LGTM! Thanks

clang/lib/Headers/opencl-c.h

 
 /**
  * Returns fast_length(p0 - p1).
  */
 float __ovld __cnfn fast_distance(float, float);
 float __ovld __cnfn fast_distance(float2, float2);
 float __ovld __cnfn fast_distance(float3, float3);
 float __ovld __cnfn fast_distance(float4, float4);
-#ifdef cl_khr_fp16
-half __ovld __cnfn fast_distance(half, half);
-half __ovld __cnfn fast_distance(half2, half2);
-half __ovld __cnfn fast_distance(half3, half3);
-half __ovld __cnfn fast_distance(half4, half4);
-#endif //cl_khr_fp16
 
 /**
  * Returns the length of vector p computed as:
  * half_sqrt(p.x2 + p.y2 + ...)
  */
 float __ovld __cnfn fast_length(float);
 float __ovld __cnfn fast_length(float2);
 float __ovld __cnfn fast_length(float3);
 float __ovld __cnfn fast_length(float4);
-#ifdef cl_khr_fp16
-half __ovld __cnfn fast_length(half);
-half __ovld __cnfn fast_length(half2);
-half __ovld __cnfn fast_length(half3);
-half __ovld __cnfn fast_length(half4);
-#endif //cl_khr_fp16
 
 /**
  * Returns a vector in the same direction as p but with a
  * length of 1. fast_normalize is computed as:
  * p * half_rsqrt (p.x^2 + p.y^2 + ... )
  * The result shall be within 8192 ulps error from the
  * infinitely precise result of
  * if (all(p == 0.0f))

  * mode, individual operand elements with magnitude
  * less than sqrt(FLT_MIN) may be flushed to zero
  * before proceeding with the calculation.
  */
 float __ovld __cnfn fast_normalize(float);
 float2 __ovld __cnfn fast_normalize(float2);
 float3 __ovld __cnfn fast_normalize(float3);
 float4 __ovld __cnfn fast_normalize(float4);
-#ifdef cl_khr_fp16
-half __ovld __cnfn fast_normalize(half);
-half2 __ovld __cnfn fast_normalize(half2);
-half3 __ovld __cnfn fast_normalize(half3);
-half4 __ovld __cnfn fast_normalize(half4);
-#endif //cl_khr_fp16
 
 // OpenCL v1.1 s6.11.6, v1.2 s6.12.6, v2.0 s6.13.6 - Relational Functions
 
 /**
  * intn isequal (floatn x, floatn y)
  * Returns the component-wise compare of x == y.
  */
 int __ovld __cnfn isequal(float, float);