Replace M_PI with C++ numbers

C++20 added π (pi) to the standard, replace the C macro globally.

Signed-off-by: Ralph Sennhauser <ralph.sennhauser@gmail.com>

source/renderer/TexturedLineRData.cpp

@@ -1,4 +1,4 @@
-/* Copyright (C) 2025 Wildfire Games.
+/* Copyright (C) 2026 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
@@ -43,6 +43,7 @@
 #include <cmath>
 #include <cstddef>
 #include <cstdint>
+#include <numbers>
 
 /* Note: this implementation uses CVertexBufferManager directly rather than access it through the nicer VertexArray interface,
  * because it allows you to work with variable amounts of vertices and indices more easily. New code should prefer
@@ -410,7 +411,7 @@ void CTexturedLineRData::CreateLineCap(const SOverlayTexturedLine& line, const C
 			// To please OpenGL's winding order, this angle needs to be negated depending on whether we start rotating from
 			// the (center -> corner1) or (center -> corner2) vector. For the (center -> corner2) vector, we apparently need to use
 			// the negated angle.
-			float stepAngle = -(float)(M_PI/(roundCapPoints-1));
+			float stepAngle = -std::numbers::pi_v<float> / (roundCapPoints-1);
 
 			// Push the vertices in triangle fan order (easy to generate GL_TRIANGLES indices for afterwards)
 			// Note that we're manually adding the corner vertices instead of having them be generated by the rotating vector.