Unsetting ac_cv_{func,lib}_* is bad, you can't feed the configure cache.
Terminate them with extreme prejudice.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>

diff -Nura php-5.6.8.orig/acinclude.m4 php-5.6.8/acinclude.m4
--- php-5.6.8.orig/acinclude.m4	2015-04-15 20:05:57.000000000 +0200
+++ php-5.6.8/acinclude.m4	2015-05-18 20:03:50.833099001 +0200
@@ -1897,8 +1897,6 @@
 dnl
 AC_DEFUN([PHP_CHECK_FUNC_LIB],[
   ifelse($2,,:,[
-  unset ac_cv_lib_$2[]_$1
-  unset ac_cv_lib_$2[]___$1
   unset found
   AC_CHECK_LIB($2, $1, [found=yes], [
     AC_CHECK_LIB($2, __$1, [found=yes], [found=no])
@@ -1930,8 +1928,6 @@
 dnl Defines HAVE_func and HAVE_library if found and adds the library to LIBS.
 dnl
 AC_DEFUN([PHP_CHECK_FUNC],[
-  unset ac_cv_func_$1
-  unset ac_cv_func___$1
   unset found
   
   AC_CHECK_FUNC($1, [found=yes],[ AC_CHECK_FUNC(__$1,[found=yes],[found=no]) ])