fixing ax_check_gl macro
respect GL_LDFLAGS

not only GL_LIBS
added GL_LDFLAGS

since the new ax-macros also define these
(e.g. on OSX)
added GL_LDFLAGS/GLUT_LDFLAGS

since the new ax-macros also define these (e.g. on OSX)
Fixed no-X detection for darwin's GL
trying to make AX_CHECK_GLU work on OSX
fix AX_CHECK_GLUT as well