build: cleaning up configure script to comply with more recent autoconf documentation
build: cleaning up configure script to comply with more recent autoconf documentation

cjcliffe/liquid-dsp,biotrump/liquid-dsp,wangning223/liquid-dsp,cjcliffe/liquid-dsp,wangning223/liquid-dsp,jgaeddert/liquid-dsp,biotrump/liquid-dsp,wangning223/liquid-dsp,wangning223/liquid-dsp,manuts/liquid-dsp,manuts/liquid-dsp,cjcliffe/liquid-dsp,jgaeddert/liquid-dsp,jgaeddert/liquid-dsp,andrepuschmann/liquid-dsp,andrepuschmann/liquid-dsp,JayKickliter/liquid-dsp,biotrump/liquid-dsp,jgaeddert/liquid-dsp,manuts/liquid-dsp,cjcliffe/liquid-dsp,biotrump/liquid-dsp,JayKickliter/liquid-dsp,manuts/liquid-dsp,cjcliffe/liquid-dsp,andrepuschmann/liquid-dsp,andrepuschmann/liquid-dsp,JayKickliter/liquid-dsp,JayKickliter/liquid-dsp,andrepuschmann/liquid-dsp,biotrump/liquid-dsp,wangning223/liquid-dsp,jgaeddert/liquid-dsp,manuts/liquid-dsp,JayKickliter/liquid-dsp