Part 2 of 3 commits bringing proper Doxygen path usage without use of @wxheader.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@54386 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/doxygen/regen.sh

@@ -20,6 +20,7 @@ me=$(basename $0)
 path=${0%%/$me}        # path from which the script has been launched
 current=$(pwd)
 cd $path
+WXWIDGETS=`cd ../.. && pwd`
 
 # prepare folders for the cp commands below
 mkdir -p out/html       # we need to copy files in this folder below