configure: improve error message for missing yasm

Originally committed as revision 24951 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -2571,8 +2571,7 @@ EOF
     esac
     if ! disabled_any asm mmx yasm; then
         check_yasm "pabsw xmm0, xmm0" && enable yasm ||
-            die "yasm not found, performance will suffer. " \
-            "If you really want to compile without yasm, configure with --disable-yasm."
+            die "yasm not found, use --disable-yasm for a crippled build"
     fi
 
     case "$cpu" in