Makefile: Stop creating '-d' directory

Install-common section was creating superfluous '-d' directory in build
location.

Split the directory creation into individual install commands to cope
with cross platform differences of interpreting subsequent '-d'
arguments.  e.g. GNU appears to be fine.  Apple creates the stray
directory.
Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>

Makefile

@@ -100,7 +100,8 @@ clean : mostly_clean
 install : all install-common
 
 install-common :
-	$(INSTALL) -d $(DESTDIR)$(BINDIR) -d $(DESTDIR)$(MANDIR)/man8
+	$(INSTALL) -d $(DESTDIR)$(BINDIR)
+	$(INSTALL) -d $(DESTDIR)$(MANDIR)/man8
 	$(INSTALL) -m 644 $(MAN)/dnsmasq.8 $(DESTDIR)$(MANDIR)/man8 
 	$(INSTALL) -m 755 $(BUILDDIR)/dnsmasq $(DESTDIR)$(BINDIR)