[build] Drop timestamps from .a file

Make the contents of $(BLIB) deterministic to allow it to be
subsequently used for calculating a build ID.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/Makefile.housekeeping

diff --git a/src/Makefile.housekeeping b/src/Makefile.housekeeping
index cac6efc..1155a0e 100644
--- a/src/Makefile.housekeeping
+++ b/src/Makefile.housekeeping
@@ -1156,8 +1156,8 @@
 $(BLIB) : $(BLIB_OBJS) $(BLIB_LIST) $(MAKEDEPS)
 	$(Q)$(RM) $(BLIB)
 	$(QM)$(ECHO) "  [AR] $@"
-	$(Q)$(AR) r $@ $(sort $(BLIB_OBJS))
-	$(Q)$(RANLIB) $@
+	$(Q)$(AR) rD $@ $(sort $(BLIB_OBJS))
+	$(Q)$(RANLIB) -D $@
 blib : $(BLIB)
 
 # Command to generate build ID.  Must be unique for each $(BIN)/%.tmp,