configure: handle xargs versions that exec empty commands

Some versions of xargs don't run any commands if no input is given,
others do run it at least once, causing errors.
Pass -r to xargs to avoid that behaviour and never run empty commands.

configure

@@ -5037,7 +5037,7 @@ probe_cc(){
             _ident=$($_cc --version 2>/dev/null | head -n1 | tr -d '\r')
         fi
         if [ -x "$(command -v wslpath)" ]; then
-            _DEPCMD='$(DEP$(1)) $(DEP$(1)FLAGS) $($(1)DEP_FLAGS) $< 2>&1 | awk '\''/including/ { sub(/^.*file: */, ""); if (!match($$0, / /)) { print $$0 } }'\'' | xargs -d\\n -n1 wslpath -u | awk '\''BEGIN { printf "%s:", "$@" }; { sub(/\r/,""); printf " %s", $$0 }; END { print "" }'\'' > $(@:.o=.d)'
+            _DEPCMD='$(DEP$(1)) $(DEP$(1)FLAGS) $($(1)DEP_FLAGS) $< 2>&1 | awk '\''/including/ { sub(/^.*file: */, ""); if (!match($$0, / /)) { print $$0 } }'\'' | xargs -r -d\\n -n1 wslpath -u | awk '\''BEGIN { printf "%s:", "$@" }; { sub(/\r/,""); printf " %s", $$0 }; END { print "" }'\'' > $(@:.o=.d)'
 
         else
             _DEPCMD='$(DEP$(1)) $(DEP$(1)FLAGS) $($(1)DEP_FLAGS) $< 2>&1 | awk '\''/including/ { sub(/^.*file: */, ""); gsub(/\\/, "/"); if (!match($$0, / /)) print "$@:", $$0 }'\'' > $(@:.o=.d)'