fix compilation of 3dnowext instinsincs, both on ia32 and AMD64.

3dnow intrinsincs are for now only compiled if 3dnowext support is available. (I should add smth that
checks for plain 3dnow later)

Originally committed as revision 5386 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -1114,13 +1114,19 @@ fi
 cat > $TMPC << EOF
 #include <mm3dnow.h>
 int main(void) {
+__m64 b1;
+b1 = _m_pswapd(b1);
 _m_femms();
 return 0;
 }
 EOF
 
 mm3dnow=no
-if $cc -m3dnow -o $TMPO $TMPC 2> /dev/null ; then
+march=athlon
+if test "$cpu" = "x86_64"; then
+  march=k8
+fi
+if $cc -march=$march -o $TMPO $TMPC 2> /dev/null ; then
   mm3dnow=yes
 fi
 

libavcodec/Makefile

@@ -350,7 +350,12 @@ depend: CFLAGS+= -msse
 endif
 ifdef TARGET_BUILTIN_3DNOW
 i386/fft_3dn.o: CFLAGS+= -m3dnow
-i386/fft_3dn2.o: CFLAGS+= -m3dnow
+ifeq ($(TARGET_ARCH_X86),yes)
+i386/fft_3dn2.o: CFLAGS+= -march=athlon
+endif
+ifeq ($(TARGET_ARCH_X86_64),yes)
+i386/fft_3dn2.o: CFLAGS+= -march=k8
+endif
 endif
 endif