Only update PKG_CONFIG_PATH if the directory exists

[[Imported from SVN: r6427]]

bin/dunecontrol

@@ -80,12 +80,14 @@ fi
 
 export PREFIX_DIR="`canonicalpath $0`/.."
 
+# create PKG_CONFIG_PATH for installed dune modules
+if test -d "$PREFIX_DIR/lib/pkgconfig"; then
+  export PKG_CONFIG_PATH="$PKG_CONFIG_PATH:$PREFIX_DIR/lib/pkgconfig"
+fi
+
 # Read the modules find part
 . "$PREFIX_DIR/lib/dunemodules.lib"
 
-# create PKG_CONFIG_PATH for installed dune modules
-export PKG_CONFIG_PATH="$PKG_CONFIG_PATH:`canonicalpath $0`/../lib/pkgconfig"
-
 ###############################################
 
 onbuildfailure() {