Robustify source directory check.

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@3960 c046a42c-6fe2-441c-8c8c-71466251a162

configure

@@ -207,16 +207,12 @@ fi
 source_path=`dirname "$0"`
 source_path_used="no"
 workdir=`pwd`
-workdir=`readlink -f $workdir`
 if [ -z "$source_path" ]; then
     source_path=$workdir
 else
     source_path=`cd "$source_path"; pwd`
-    source_path=`readlink -f $source_path`
-    if test "$source_path" != "$workdir" ; then
-        source_path_used="yes"
-    fi
 fi
+[ -f "$workdir/vl.c" ] || source_path_used="yes"
 
 werror="no"
 # generate compile errors on warnings for development builds