See the followings for the origin of this patch
http://www.linuxfromscratch.org/blfs/view/svn/multimedia/libmad.html
http://www.linuxfromscratch.org/patches/blfs/svn/libmad-0.15.1b-fixes-1.patch
--- src/libmad/configure	2004-02-05 09:34:07.000000000 +0000
+++ src/libmad/configure.new	2020-06-30 21:10:28.528018931 +0000
@@ -19083,71 +19083,7 @@
 
 if test "$GCC" = yes
 then
-    if test -z "$arch"
-    then
-	case "$host" in
-	    i386-*)           ;;
-	    i?86-*)           arch="-march=i486" ;;
-	    arm*-empeg-*)     arch="-march=armv4 -mtune=strongarm1100" ;;
-	    armv4*-*)         arch="-march=armv4 -mtune=strongarm" ;;
-	    powerpc-*)        ;;
-	    mips*-agenda-*)   arch="-mcpu=vr4100" ;;
-	    mips*-luxsonor-*) arch="-mips1 -mcpu=r3000 -Wa,-m4010" ;;
-	esac
-    fi
-
-    case "$optimize" in
-	-O|"-O "*)
-	    optimize="-O"
-	    optimize="$optimize -fforce-mem"
-	    optimize="$optimize -fforce-addr"
-	    : #x optimize="$optimize -finline-functions"
-	    : #- optimize="$optimize -fstrength-reduce"
-	    optimize="$optimize -fthread-jumps"
-	    optimize="$optimize -fcse-follow-jumps"
-	    optimize="$optimize -fcse-skip-blocks"
-	    : #x optimize="$optimize -frerun-cse-after-loop"
-	    : #x optimize="$optimize -frerun-loop-opt"
-	    : #x optimize="$optimize -fgcse"
-	    optimize="$optimize -fexpensive-optimizations"
-	    optimize="$optimize -fregmove"
-	    : #* optimize="$optimize -fdelayed-branch"
-	    : #x optimize="$optimize -fschedule-insns"
-	    optimize="$optimize -fschedule-insns2"
-	    : #? optimize="$optimize -ffunction-sections"
-	    : #? optimize="$optimize -fcaller-saves"
-	    : #> optimize="$optimize -funroll-loops"
-	    : #> optimize="$optimize -funroll-all-loops"
-	    : #x optimize="$optimize -fmove-all-movables"
-	    : #x optimize="$optimize -freduce-all-givs"
-	    : #? optimize="$optimize -fstrict-aliasing"
-	    : #* optimize="$optimize -fstructure-noalias"
-
-	    case "$host" in
-		arm*-*)
-		    optimize="$optimize -fstrength-reduce"
-		    ;;
-		mips*-*)
-		    optimize="$optimize -fstrength-reduce"
-		    optimize="$optimize -finline-functions"
-		    ;;
-		i?86-*)
-		    optimize="$optimize -fstrength-reduce"
-		    ;;
-		powerpc-apple-*)
-		    # this triggers an internal compiler error with gcc2
-		    : #optimize="$optimize -fstrength-reduce"
-
-		    # this is really only beneficial with gcc3
-		    : #optimize="$optimize -finline-functions"
-		    ;;
-		*)
-		    # this sometimes provokes bugs in gcc 2.95.2
-		    : #optimize="$optimize -fstrength-reduce"
-		    ;;
-	    esac
-	    ;;
-    esac
+    optimize="-O2"
 fi
 
 case "$host" in
@@ -21497,6 +21433,7 @@
 then
     case "$host" in
 	i?86-*)     FPM="INTEL"  ;;
+	x86_64*)    FPM="64BIT"  ;;
 	arm*-*)     FPM="ARM"    ;;
 	mips*-*)    FPM="MIPS"   ;;
 	sparc*-*)   FPM="SPARC"  ;;