Fix a bug in the CMake build that caused APR and APR-Util libraries to
become "not found" after they had already been found in a non-default
library path, when Serf is built as part of a larger project.

* build/FindAPR.cmake (_apru_location): Unset the _dir, _lib and _extra
   local variables so that they don't inherit unhelpful strange values
   from any parent CMake environments.


git-svn-id: https://svn.apache.org/repos/asf/serf/trunk@1844404 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/build/FindAPR.cmake b/build/FindAPR.cmake
index af7b36e..073ffe7 100644
--- a/build/FindAPR.cmake
+++ b/build/FindAPR.cmake
@@ -126,6 +126,9 @@
 
 # From the list of link libraries, extract the imported location
 function(_apru_location _location_var _extralibs_var)
+  unset(_dir)
+  unset(_lib)
+  unset(_extra)
   foreach(_part ${ARGN})
     string(SUBSTRING "${_part}" 0 2 _flag)
     if(_flag STREQUAL "-L")