Fixes in build systems for autotools and cmake, see Issue 438

Thanks to Daniel KO Listas at the ODE mailing list
Don't build graphics demos when OpenGL or GLUT is not found
CMake will still build the non-graphical HelloWorld demo (output text to console)

Fix linker error: ThreadingDemo requires pthreads on UNIX systems
Thanks to reptor, see also http://bulletphysics.org/Bullet/phpBB3/posting.php?mode=reply&f=9&t=5748

configure.ac

@@ -81,10 +81,53 @@ AM_CONDITIONAL([CONDITIONAL_BUILD_MULTITHREADED], [test "$build_multithreaded" =
 
 AC_ARG_ENABLE([demos],
     [AS_HELP_STRING([--disable-demos],
-	    [disable Bullet demos])],
+            [disable Bullet demos])],
     [],
     [enable_demos=yes])
 AM_CONDITIONAL([CONDITIONAL_BUILD_DEMOS], [false])
+
+dnl Check for OpenGL and GLUT
+if test "x$drawstuff" = "xOSX"; then
+  AC_DEFINE([HAVE_APPLE_OPENGL_FRAMEWORK], [1],
+            [Use the Apple OpenGL framework.])
+  GL_LIBS="-framework GLUT -framework OpenGL -framework Carbon -framework AGL"
+  have_glut=yes
+else
+  have_gl_headers=yes
+  AC_CHECK_HEADERS(GL/gl.h GL/glu.h GL/glext.h GL/glut.h, ,
+        [have_gl_headers=no],
+       [[#ifdef WIN32
+         #include <windows.h>
+         #endif
+         #if HAVE_GL_GL_H
+         #include <GL/gl.h>
+         #endif
+             #if HAVE_GL_GLU_H
+         #include <GL/glu.h>
+         #endif
+       ]])
+  have_gl=no
+  have_glu=no
+  have_glut=no
+  TEMP_LDFLAGS="$LDFLAGS"
+  AC_CHECK_LIB(GL, main, [GL_LIBS="-lGL"; have_gl=yes])
+  AC_CHECK_LIB(GLU, main, [GL_LIBS="-lGLU $GL_LIBS"; have_glu=yes], , -lGL)
+  AC_CHECK_LIB(GLUT, main, [GL_LIBS="-lGLUT -LGLU  $GL_LIBS"; have_glut=yes], ,-lGLUT)
+  AC_CHECK_LIB(opengl32, main, [GL_LIBS="-lopengl32"; have_gl=yes])
+  AC_CHECK_LIB(glu32, main, [GL_LIBS="-lglu32 $GL_LIBS"; have_glu=yes], , -lopengl32)
+  LDFLAGS="$TEMP_LDFLAGS"
+  if test $have_gl = no -o $have_glu = no -o $have_gl_headers = no; then
+    if test x$enable_demos = xyes; then
+      AC_MSG_WARN([Demos and Extras will not be built because OpenGL and GLUT doesn't seem to work. See `config.log' for details.])
+    fi
+    enable_demos=no
+  else
+  AC_MSG_NOTICE([Found OpenGL])
+  fi
+fi
+AC_SUBST(GL_LIBS)
+
+
 if test "x$enable_demos" != xno; then
     AC_MSG_NOTICE([Building Bullet demos])
     AM_CONDITIONAL([CONDITIONAL_BUILD_DEMOS],[true])