This patch implements builtins for the following prototypes:

vector signed char vec_blendv (vector signed char, vector signed char, vector unsigned char);

vector unsigned char vec_blendv (vector unsigned char, vector unsigned char, vector unsigned char);

vector signed short vec_blendv (vector signed short, vector signed short, vector unsigned short);

vector unsigned short vec_blendv (vector unsigned short, vector unsigned short, vector unsigned short);

vector signed int vec_blendv (vector signed int, vector signed int, vector unsigned int);

vector unsigned int vec_blendv (vector unsigned int, vector unsigned int, vector unsigned int);

vector signed long long vec_blendv (vector signed long long, vector signed long long, vector unsigned long long);

vector unsigned long long vec_blendv (vector unsigned long long, vector unsigned long long, vector unsigned long long);

vector float vec_blendv (vector float, vector float, vector unsigned int);

vector double vec_blendv (vector double, vector double, vector unsigned long long);