Some math functions need to be implemented

[yu810226]

• clamp, degrees, max, min, mix, radians, step, smoothstep, sign, acospi, asinpi, atanpi, atan2pi, cospi, fract, ilogb, ldexp, lgamma_r, mad, maxmag, minmag, nan, nextafter, pown, powr, rootn, rsqrt, sincos, sinpi, tanpi, cross, dot, distance, length, normalize, fast_distance, fast_length, fast_normalize, abs_diff, add_sat, hadd, rhadd, clz, mad_hi, mad_sat, mul_hi, sub_sat, upsample, popcount, mas24, mul24 are not implemented.
• Native function divide, exp10, powr, recip, recip are not implemented.
• Relational functions are not supported now.