Fix for libao dlsym_auto_underscore on Mac OS X

libao is a cross-platform audio output library used by, among others, ogg123. When libao-0.8.8 is built on Mac OS X, trying to run ogg123 meets with this complaint:

dyld: lazy symbol binding failed: Symbol not found:
_dlsym_auto_underscore
  Referenced from: /usr/local/lib/libao.2.dylib
  Expected in: flat namespace

I'm not sure, but I think the dlsym_auto_underscore was required in previous versions of Mac OS X, but for me on 10.4.9 it worked to simply remove it from the darwin CFLAGS setting in the configure script:

From this:

        *-darwin*)
                PLUGIN_LDFLAGS="-module -avoid-version"
                DEBUG="-g -Wall -D__NO_MATH_INLINES
-fsigned-char -Ddlsym=dlsym_auto_underscore"
                CFLAGS="-D__NO_MATH_INLINES -fsigned-char
-Ddlsym=dlsym_auto_underscore"
                PROFILE="-g -pg -D__NO_MATH_INLINES
-fsigned-char -Ddlsym=dlsym_auto_underscore" ;;

To this:

        *-darwin*)
                PLUGIN_LDFLAGS="-module -avoid-version"
                DEBUG="-g -Wall -D__NO_MATH_INLINES
-fsigned-char"
                CFLAGS="-D__NO_MATH_INLINES -fsigned-char"
                PROFILE="-g -pg -D__NO_MATH_INLINES
-fsigned-char" ;;