configure: Use the right variables in check_host_cpp

HOSTCPPFLAGS and HOSTCFLAGS are only set in config.mak.
Signed-off-by: Martin Storsjö <martin@martin.st>

configure

@@ -1067,7 +1067,7 @@ check_host_cpp(){
     log check_host_cpp "$@"
     cat > $TMPC
     log_file $TMPC
-    check_cmd $host_cc $HOSTCPPFLAGS $HOSTCFLAGS "$@" $(hostcc_e $TMPO) $TMPC
+    check_cmd $host_cc $host_cppflags $host_cflags "$@" $(hostcc_e $TMPO) $TMPC
 }
 
 check_host_cppflags(){