Add the installation bin directory to the path internally in wrapper scripts

This allows invoking the script frontends via an explicit path,
without adding the directory to the PATH environment variable before
calling them.

wrappers/windres-wrapper.sh

@@ -27,6 +27,9 @@
 #
 # For more information, please refer to <http://unlicense.org/>
 
+DIR="$(cd "$(dirname "$0")" && pwd)"
+export PATH=$DIR:$PATH
+
 print_version () {
     cat <<EOF >&2
 version: LLVM windres (GNU Binutils compatible) 0.1