BUILD: fix "make install" to support spaces in the install dirs

Makefile is unable to install into directories containing spaces.
diff --git a/Makefile b/Makefile
index 0d1d13a..ac93fed 100644
--- a/Makefile
+++ b/Makefile
@@ -710,19 +710,19 @@
 	$(CC) $(COPTS) -DDEFAULT_MMAP_THRESHOLD=$(DLMALLOC_THRES) -c -o $@ $<
 
 install-man:
-	install -d $(DESTDIR)$(MANDIR)/man1
-	install -m 644 doc/haproxy.1 $(DESTDIR)$(MANDIR)/man1
+	install -d "$(DESTDIR)$(MANDIR)"/man1
+	install -m 644 doc/haproxy.1 "$(DESTDIR)$(MANDIR)"/man1
 
 install-doc:
-	install -d $(DESTDIR)$(DOCDIR)
+	install -d "$(DESTDIR)$(DOCDIR)"
 	for x in configuration architecture haproxy-en haproxy-fr; do \
-		install -m 644 doc/$$x.txt $(DESTDIR)$(DOCDIR) ; \
+		install -m 644 doc/$$x.txt "$(DESTDIR)$(DOCDIR)" ; \
 	done
 
 install-bin: haproxy haproxy-systemd-wrapper
-	install -d $(DESTDIR)$(SBINDIR)
-	install haproxy $(DESTDIR)$(SBINDIR)
-	install haproxy-systemd-wrapper $(DESTDIR)$(SBINDIR)
+	install -d "$(DESTDIR)$(SBINDIR)"
+	install haproxy "$(DESTDIR)$(SBINDIR)"
+	install haproxy-systemd-wrapper "$(DESTDIR)$(SBINDIR)"
 
 install: install-bin install-man install-doc