Add overloads for new and delete to avoid linking to libstdc++

We could indeed add this library to our pkg-config file, but we don't
use any other of its functions, and using malloc() and free() is more
efficient anyway.

src/pixel_stream.h

@@ -79,6 +79,9 @@ struct PixelStreamBase {
     virtual void write(GXColor color) = 0;
     virtual void setup() {}
 
+    void *operator new(size_t size) { return malloc(size); }
+    void operator delete(void * p) { free(p); }
+
 protected:
     void *m_data;
     int m_width;

src/texel.h

@@ -72,6 +72,9 @@ struct Texel {
         }
     }
 
+    void *operator new(size_t size) { return malloc(size); }
+    void operator delete(void * p) { free(p); }
+
     void *m_data;
     int m_x;
     int m_y;