games/solver: Math training game using C and SDL2

Solver is a math training game. The goal of the game is to improve the
user's confidence in using four basic math operations: addition,
subtraction, multiplication and division. The user can set various
options to create a custom game experience. These options include
setting the time limit and the goal for correct/incorrect answers.
This program uses C and SDL2.

PR: 267373
Reported by: modex@danwin1210.de