Deal correctly with wx directory being a symlink in docs generation script.

The script calling Doxygen is smart enough to strip the path of the wxWidgets
directory from the paths of the files, but it didn't do it correctly if this
directory was a symlink.

Fix this by using readlink, if available, to get the canonical name.

Closes #14796.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72839 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/doxygen/regen.sh

@@ -20,12 +20,20 @@ me=$(basename $0)
 path=${0%%/$me}        # path from which the script has been launched
 current=$(pwd)
 cd $path
-if [ "$WXWIDGETS" = "" ]; then
-    export WXWIDGETS=`cd ../.. && pwd`
-    if [ "$OSTYPE" = "cygwin" ]; then
-        export WXWIDGETS=`cygpath -w $WXWIDGETS`
+if [[ -z "$WXWIDGETS" ]]; then
+    WXWIDGETS=`cd ../.. && pwd`
+    # Use the real path in case it's a symlink
+    if command -v readlink; then
+        normalized=`readlink -e $WXWIDGETS`
+        if [[ -n $normalized ]]; then
+            WXWIDGETS=$normalized
         fi
     fi 
+    if [ "$OSTYPE" = "cygwin" ]; then
+        WXWIDGETS=`cygpath -w $WXWIDGETS`
+    fi
+    export WXWIDGETS
+fi
 
 if [ "$DOXYGEN" = "" ]; then
     DOXYGEN=doxygen