VPATH builds were broken, if the user specified the path to configure

using an absolute path. With this change, absolute and relative paths
are accepted and processed correctly.

acinclude.m4

@@ -404,8 +404,8 @@ dnl "shared" can be set to "shared" or "yes" to build the extension as
 dnl a dynamically loadable library.
 dnl
 AC_DEFUN(PHP_EXTENSION,[
-  if test -d "$cwd/$srcdir/ext/$1" ; then
-    ext_src_base="${abs_srcdir}/ext/$1/"
+  if test -d "$abs_srcdir/ext/$1" ; then
+    ext_src_base="$abs_srcdir/ext/$1/"
     ext_base="ext/$1/"
     EXT_SUBDIRS="$EXT_SUBDIRS $1"
     if test "$2" != "shared" && test "$2" != "yes" && test -z "$php_always_shared"; then