Lift is created when there's a relative airflow over the wing. In order to produce lift, this airflow has to be from the front to the rear (leading edge to trailing edge). The Pitot Tube points forward, to measure the pressure due to the impact of air molecules from that direction, ie the relative airflow component flowing from the direction to which it points
The Pitot of a stationary airplane on a runway facing a 50kt headwind will register a dynamic pressure to show an Indicated Airspeed of 50KIAS. If the airplane requires a take off (rotation) speed of 65KIAS, it needs to accelerate to a speed of 15kts relative to the runway as would be measured by an automobile speedometer based on wheel/tyre rpm. At this 15kts, the IAS would read 65KIAS enabling the airplane to get airborne.
Facing the opposite direction with the 50kts blowing from tail to nose, the stationary airplane would not indicate any IAS till it achieves 50kts relative to the ground as measured by the hypothetical automobile speedometer. Thereafter, accelerating further, the Pitot would start registering dynamic pressure and it would start registering IAS therefore. So the automobile speedometer would read 50 + 65 = 115kts for the IAS to be at 65KIAS.
The difference between the 2 take-offs above is in the distance required for the take-offs and the automobile speedometer represents the same as forward Ground Speed.
Once airborne, in line with what you stated, the airplane loses it's 'tethering' to the ground and shear conditions excepted, the direction of flight relative to the wind will not cause problems such as stalling the airplane.
(Shear conditions are defined by rapid changes to the flow of the air with relation to the air mass itself. Such conditions exist due to terrain, jet-streams, Fronts, storm conditions man made obstacles and related phenomena.)