m4/xc-cc-check.m4: use XC_CHECK_BUILD_FLAGS (#236)

Use XC_CHECK_BUILD_FLAGS instead of XC_CHECK_USER_FLAGS.
Otherwise it complains of CPPFLAGS in CFLAGS.
[Retrieved from:
https://git.buildroot.net/buildroot/tree/package/c-ares/0001-use_check_build_instead_of_check_user.patch]

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Submitted by: Fabrice Fontaine

m4/xc-cc-check.m4

@@ -59,7 +59,7 @@ dnl Private macro.
 
 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