FindPHP4: Drop extra content from reported PHP4_INCLUDE_PATH (#14540)

The set() call for this variable left out the CACHE keyword.  It does
not need to be cached anyway, so drop the other CACHE set() signature
arguments.

Bug-Debian: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=722475
Reported-by: Modestas Vainius <modax@debian.org>
Inspired-by: Mathieu Malaterre <malat@debian.org>
Merge topic 'FindPHP4-no-cache-output' into next

a06debc FindPHP4: Drop extra content from reported PHP4_INCLUDE_PATH (#14540)