Make configure subdirectories in AC_CONFIG_SUBDIRS literal.

This fixes the autoreconf warnings and follows the upstream manual:
http://www.gnu.org/savannah-checkouts/gnu/autoconf/manual/autoconf-2.69/html_node/Subdirectories.html

configure.ac

@@ -490,9 +490,7 @@ for lib in $LIBRARIES ; do
       eval BUILD_LDFLAGS=\"\$BUILD_LDFLAGS \$${lib}_LOCAL_LDFLAGS\"
       eval OPTOBJS=\"$OPTOBJS \$${lib}_LOCAL_OPTOBJS\"
       eval CXXFLAGS=\"\$CXXFLAGS \$${lib}_LOCAL_CXXFLAGS\"
-      eval CONFIG_SUBDIRS=\"\$${lib}_LOCAL_CONFIG_SUBDIRS\"
       eval ac_configure_args=\"\$ac_configure_args \$${lib}_LOCAL_CONFIGURE_ARGS\"
-      AC_CONFIG_SUBDIRS($CONFIG_SUBDIRS)
 
       eval CPPSYMBOLS=\"\$${lib}_LOCAL_CPPSYMBOLS\"
       for symbol in $CPPSYMBOLS ; do
@@ -511,6 +509,22 @@ for lib in $LIBRARIES ; do
    fi
 done
 
+AUDACITY_CONFIG_SUBDIRS_LIBFLAC
+AUDACITY_CONFIG_SUBDIRS_LIBID3TAG
+AUDACITY_CONFIG_SUBDIRS_LIBMAD
+AUDACITY_CONFIG_SUBDIRS_LIBNYQUIST
+AUDACITY_CONFIG_SUBDIRS_LIBRESAMPLE
+AUDACITY_CONFIG_SUBDIRS_LIBSAMPLERATE
+AUDACITY_CONFIG_SUBDIRS_LIBSBSMS
+AUDACITY_CONFIG_SUBDIRS_LIBSNDFILE
+AUDACITY_CONFIG_SUBDIRS_LIBSOUNDTOUCH
+AUDACITY_CONFIG_SUBDIRS_LIBSOXR
+AUDACITY_CONFIG_SUBDIRS_LIBTWOLAME
+AUDACITY_CONFIG_SUBDIRS_LIBVAMP
+AUDACITY_CONFIG_SUBDIRS_LIBVORBIS
+AUDACITY_CONFIG_SUBDIRS_PORTAUDIO
+AUDACITY_CONFIG_SUBDIRS_PORTSMF
+
 dnl " This is included purely to close an otherwise endless string in vim