Use XC_CHECK_BUILD_FLAGS instead of XC_CHECK_USER_FLAGS.
Otherwise it complains of CPPFLAGS in CFLAGS.

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

diff -Nura c-ares-1.10.0.orig/m4/xc-cc-check.m4 c-ares-1.10.0/m4/xc-cc-check.m4
--- c-ares-1.10.0.orig/m4/xc-cc-check.m4	2013-12-26 19:40:46.354195974 -0300
+++ c-ares-1.10.0/m4/xc-cc-check.m4	2013-12-26 19:41:01.850718535 -0300
@@ -59,7 +59,7 @@
 
 AC_DEFUN([_XC_PROG_CC], [
   AC_REQUIRE([_XC_PROG_CC_PREAMBLE])dnl
-  AC_REQUIRE([XC_CHECK_USER_FLAGS])dnl
+  AC_REQUIRE([XC_CHECK_BUILD_FLAGS])dnl
   AC_REQUIRE([AC_PROG_INSTALL])dnl
   AC_REQUIRE([AC_PROG_CC])dnl
   AC_REQUIRE([AM_PROG_CC_C_O])dnl