title: SDL2_Gfx - Linker issue with cygwin
body: <p>I'm struggling to compile SDL_Gfx with cygwin.
  The configure script worked without issues.</p>
  
  <p>Here's the last makefile command:</p>
  
  <pre><code>/bin/sh ./libtool --tag=CC   --mode=link gcc  -g -O2 -I/usr/local/include/SDL2 -Dmain=SDL_main -no-undefined -release 1.0 -version-info 0:1:0  -o libSDL2_gfx.la -rpath /usr/local/lib SDL2_framerate.lo SDL2_gfxPrimitives.lo SDL2_imageFilter.lo SDL2_rotozoom.lo  -L/usr/lib -lcygwin -lSDL2main -lSDL2
  libtool: link: warning: library `/usr/lib/libSDL2.la' was moved.
  </code></pre>
  
  <p>And here's the linker "warning" message.</p>
  
  <pre><code>*** Warning: linker path does not have real file for library -lSDL2main.
  *** I have the capability to make that library automatically link in when
  *** you link to this library.  But I can only do this if you have a
  *** shared version of the library, which you do not appear to have
  *** because I did check the linker path looking for a file starting
  *** with libSDL2main and none of the candidates passed a file format test
  *** using a file magic. Last file checked: /lib/libSDL2main.a
  </code></pre>
  
  <p>If i try to ignore this, I'm getting this error when I try to use the library inside my application:</p>
  
  <pre><code>In function `pixel':
  /usr/local/lib/SDL2_gfx-1.0.1/SDL2_gfxPrimitives.c:75: undefined reference  to `SDL_RenderDrawPoint'
  /usr/local/lib/SDL2_gfx-1.0.1/SDL2_gfxPrimitives.c:75:(.text+0x11): relocation truncated to fit: R_X86_64_PC32 against undefined symbol `SDL_RenderDrawPoint'
  </code></pre>
  
  <p>UPDATE: I tried to switch compiler to use mingw64 instead of cywin. I'm having a similar issue, I think this is related to libtool since I can compile an external programs with similar c/l flags without issues.</p>
  
  <p>I don't know what I can try I ran out of ideas, please help.
  Thank you</p>