Add hlsl spirv and dxil backend tests.

Author: farzonl

clang/docs/LanguageExtensions.rst

@@ -665,7 +665,7 @@ Unless specified otherwise operation(±0) = ±0 and operation(±infinity) = ±in
  T __builtin_elementwise_bitreverse(T x)     return the integer represented after reversing the bits of x     integer types
  T __builtin_elementwise_exp(T x)            returns the base-e exponential, e^x, of the specified value      floating point types
  T __builtin_elementwise_exp2(T x)           returns the base-2 exponential, 2^x, of the specified value      floating point types
- 
+
  T __builtin_elementwise_sqrt(T x)           return the square root of a floating-point number                floating point types
  T __builtin_elementwise_roundeven(T x)      round x to the nearest integer value in floating point format,   floating point types
                                              rounding halfway cases to even (that is, to the nearest value