Steel wind strike's spell description (XGtE, p. 166) states:
You flourish the weapon used in the casting and then vanish to strike like the wind. Choose up to five creatures you can see within range. Make a melee spell attack against each target. On a hit, a target takes 6d10 force damage.
Now, we know that steel wind strike isn't a melee weapon attack. Attacks can either be a melee or a ranged attack and they can either be a spell or a weapon attack (so 4 types total). Sometimes it matters, but for the purposes of this question, I wanted to get that out of the way. Jeremy Crawford confirms this.
My question is in regards to the Great Weapon Fighting fighting style and the Great Weapon Master feat, both of which have similar wording.
The Great Weapon Fighting fighting style is described as follows (emphasis mine):
When you roll a 1 or 2 on a damage die for an attack you make with a melee weapon that you are wielding with two hands, you can reroll the die and must use the new roll, even if the new roll is a 1 or a 2. The weapon must have the Two-Handed or Versatile property for you to gain this benefit.
The Great Weapon Master feat (PHB, p. 167) is described as follows (emphasis mine)
On your turn, when you score a critical hit with a melee weapon or reduce a creature to 0 hit points with one, you can make one melee weapon attack as a bonus action.
Before you make a melee attack with a heavy weapon that you are proficient with, you can choose to take a -5 penalty to the attack roll. If the attack hits, you add +10 to the attack's damage.
In my mind, this all hinges on whether or not steel wind strike is considered to be using your weapon or not. All other requirements are satisfied. You are making a melee attack (weapon attack is not specified) with steel wind strike's melee spell attack, which satisfies Great Weapon Master. You are obviously making an attack, so Great Weapon Fighting is satisfied.
This leads me to conclude that if I am using that weapon, I can take a penalty for +10 damage on the spell effect, I can reroll 1s and 2s for the damage dice rolled, and if I kill something I can make a single melee weapon attack as a bonus action.
The question is: Are you making these attacks with a weapon?