Simplify libxmlrpc bundling and building

The xmlrpc library is a forked, modified and bundled into the PHP source
code. Instead of having a separate *nix build system files in the xmlrpc
library this patch removes unneeded build checks.

- AC_PROG_CC is not needed to be called by the extension itself since it
  is already part of the main configure.ac and the phpize's
  configure.ac.
- UNDEF_THREADS_HACK is not used in the current codebase.
- Symbols defined by XMLRPC_HEADER_CHECKS are not used in the current
  code.
- Symbols defined by XMLRPC_FUNCTION_CHECKS are not used in the current
  code.
- AC_PROG_RANLIB is already done by the TSRM's files and isn't needed
  for the xmlrpc extension to work.
- AC_PROG_LN_S is already done by the PHP main configure.ac and also
  isn't needed by the xmlrpc extension to be built.

ext/xmlrpc/config.m4

@@ -1,10 +1,5 @@
 dnl config.m4 for extension xmlrpc
 
-sinclude(ext/xmlrpc/libxmlrpc/acinclude.m4)
-sinclude(ext/xmlrpc/libxmlrpc/xmlrpc.m4)
-sinclude(libxmlrpc/acinclude.m4)
-sinclude(libxmlrpc/xmlrpc.m4)
-
 PHP_ARG_WITH([xmlrpc],
   [for XMLRPC-EPI support],
   [AS_HELP_STRING([[--with-xmlrpc[=DIR]]],
@@ -80,7 +75,6 @@ if test "$PHP_XMLRPC" != "no"; then
 fi
 
 if test "$PHP_XMLRPC" = "yes"; then
-  XMLRPC_CHECKS
   PHP_NEW_EXTENSION(xmlrpc,xmlrpc-epi-php.c libxmlrpc/base64.c \
           libxmlrpc/simplestring.c libxmlrpc/xml_to_dandarpc.c \
           libxmlrpc/xmlrpc_introspection.c libxmlrpc/encodings.c \