configure: Do not overwrite src symlink if it already exists.

Allows running fate from out-of-tree builds on wsl.

configure

@@ -3742,6 +3742,8 @@ mkdir -p ffbuild
 # find source path
 if test -f configure; then
     source_path=.
+elif test -f src/configure; then
+    source_path=src
 else
     source_path=$(cd $(dirname "$0"); pwd)
     case "$source_path" in
@@ -5416,7 +5418,7 @@ link_name=$(mktemp -u $TMPDIR/name_XXXXXXXX)
 mkdir "$link_dest"
 $ln_s "$link_dest" "$link_name"
 touch "$link_dest/test_file"
-if [ "$source_path" != "." ] && ([ ! -d src ] || [ -L src ]) && [ -e "$link_name/test_file" ]; then
+if [ "$source_path" != "." ] && [ "$source_path" != "src" ] && ([ ! -d src ] || [ -L src ]) && [ -e "$link_name/test_file" ]; then
     # create link to source path
     [ -e src ] && rm src
     $ln_s "$source_path" src