build: check for glBegin, which we won't end up using anyway.

configure.ac

@@ -92,6 +92,12 @@ if test "${ac_cv_my_have_gl}" = "no"; then
   AC_MSG_ERROR([[No OpenGL or OpenGL ES implementation found]])
 fi
 
+dnl Poor man's GL feature detection.
+save_LIBS="${LIBS}"
+LIBS="${LIBS} ${GL_LIBS} ${GLES2_LIBS}"
+AC_CHECK_FUNCS(glBegin)
+LIBS="${save_LIBS}"
+
 dnl Use SDL? (always required)
 ac_cv_my_have_sdl="yes"
 AC_PATH_PROG(SDL_CONFIG, sdl-config, no)

src/debugquad.cpp

@@ -388,6 +388,7 @@ void DebugQuad::TickDraw(float deltams)
     GLfloat const texcoords[] = { f1, f3, f3, f2, f2, f4,
                                   f2, f4, f4, f1, f1, f3 };
 
+#if defined HAVE_GLBEGIN
     /* Quad #1: simple glBegin program */
     glColor3f(0.8f, 0.5f, 0.2f);
     glBegin(GL_TRIANGLES);
@@ -505,8 +506,9 @@ void DebugQuad::TickDraw(float deltams)
     glDisable(GL_TEXTURE_2D);
 
     Advance();
+#endif
 
-    /* Quad #7: simple vertex buffer */
+    /* Quad #7: simple vertex buffer, no shader */
     GLfloat const vertices1[] = { data->aa.x, data->bb.y, 0.0f,
                                   data->bb.x, data->bb.y, 0.0f,
                                   data->bb.x, data->aa.y, 0.0f,