Remove redundant check for libao which causes it to always be required even if
mp3 and ogg support are disabled.

Temporarily support either mad.pc or libmad.pc to prevent breakage with future
versions of libmad. After libmad 0.16.3, new upstream renamed the pkgconfig
file to mad.pc [1], assumingly to conform to what we and most of the Linux
packagers decided upon almost 9 years ago [2], as the original libmad never
had a pkgconfig file.

[1] https://codeberg.org/tenacityteam/libmad/commit/486e615d4d8aab5b426d8b82b7dfa9867f0b2146
[2] https://cgit.freebsd.org/ports/commit/audio/libmad?id=d52971d56c7520e7b8af206bc70e05cceed295a5

--- configure.ac.orig	2023-02-03 14:46:06 UTC
+++ configure.ac
@@ -314,8 +314,10 @@ dnl Check for libao
 esac
 
 dnl Check for libao
+if test "$with_mp3_support" = yes || test "$with_ogg_support" = yes || test "$en_gcdmaster" = yes; then
 PKG_CHECK_MODULES(AO, ao >= 0.8, [AC_DEFINE(HAVE_AO,1,"")],
         [echo "gcdmaster, MP3 and Ogg support disabled"; en_gcdmaster=no; with_ogg_support=no; with_mp3_support=no])
+fi
 
 dnl Check for OGG support
 if test "$with_ogg_support" = yes; then
@@ -326,7 +328,8 @@ if test "$with_mp3_support" = yes; then
 dnl Check for MP3 support
 if test "$with_mp3_support" = yes; then
         PKG_CHECK_MODULES(MAD, mad >= 0.10, [],
-	[echo "libMAD detection via pkg-config failed"; with_mp3_support=no])
+        [PKG_CHECK_MODULES(MAD, libmad >= 0.10, [],
+	[echo "libMAD detection via pkg-config failed"; with_mp3_support=no])])
 	if test "$with_mp3_support" = no; then
 		AC_CHECK_LIB(mad, mad_stream_init, [AC_CHECK_HEADER([mad.h])])
 		if test "$ac_cv_lib_mad_mad_stream_init" = yes; then
@@ -339,12 +342,6 @@ if test "$with_mp3_support" = yes; then
 	                echo "MP3 support disabled"; with_mp3_support=no
 		fi
 	fi
-fi
-
-dnl Check for libao support
-if test "$with_mp3_support" = yes || test "$with_ogg_support" = yes || test "$en_gcdmaster" = yes; then
-PKG_CHECK_MODULES(AO, ao >= 0.8, [AC_DEFINE(HAVE_AO,1,"")],
-        [echo "Building of gcdmaster disabled"; en_gcdmaster=no])
 fi
 
 if test "$with_ogg_support" = yes; then