Revert "gdbserver/Makefile.in: add missing `-x c++`"

This reverts commit c7c9820071f8b81a64221f5cfafb3cbfeafe7916.
diff --git a/gdbserver/Makefile.in b/gdbserver/Makefile.in
index 5506701..bd6f68e 100644
--- a/gdbserver/Makefile.in
+++ b/gdbserver/Makefile.in
@@ -520,7 +520,7 @@
 	$(POSTCOMPILE)
 
 nat/%-ipa.o: ../gdb/nat/%.c
-	$(IPAGENT_COMPILE) -x c++ $<
+	$(IPAGENT_COMPILE) $<
 	$(POSTCOMPILE)
 
 %-ipa.o: ../gdb/%.c