stubdom: provide install-c target

configure --enable-c-stubdom fails to build with 'make rpmball' because
no install target exists for it. Just provide it to fix build.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: Ian Jackson <ian.jackson@eu.citrix.com>
Cc: Samuel Thibault <samuel.thibault@ens-lyon.org>
Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: Wei Liu <wei.liu2@citrix.com>
Acked-by: Samuel Thibault <samuel.thibault@ens-lyon.org>

stubdom/Makefile

@@ -472,6 +472,8 @@ install-grub: pv-grub
 	$(INSTALL_DIR) "$(DESTDIR)$(XENFIRMWAREDIR)"
 	$(INSTALL_DATA) mini-os-$(XEN_TARGET_ARCH)-grub/mini-os.gz "$(DESTDIR)$(XENFIRMWAREDIR)/pv-grub-$(XEN_TARGET_ARCH).gz"
 
+install-c: c-stubdom
+
 install-caml: caml-stubdom
 
 install-xenstore: xenstore-stubdom