stubdom: fix build with disabled pv-grub

Today the build will fail if --disable-pv-grub as a parameter of
configure, as the main Makefile will unconditionally try to build a
32-bit pv-grub stubdom.

Fix that by introducing a pv-grub-if-enabled target in
stubdom/Makefile taking care of this situation.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Reviewed-by: Ian Jackson <iwj@xenproject.org>

Makefile

@@ -72,7 +72,7 @@ build-tools-oxenstored: build-tools-public-headers
 build-stubdom: mini-os-dir build-tools-public-headers
 	$(MAKE) -C stubdom build
 ifeq (x86_64,$(XEN_TARGET_ARCH))
-	XEN_TARGET_ARCH=x86_32 $(MAKE) -C stubdom pv-grub
+	XEN_TARGET_ARCH=x86_32 $(MAKE) -C stubdom pv-grub-if-enabled
 endif
 
 .PHONY: build-docs
@@ -143,7 +143,7 @@ install-tools: install-tools-public-headers
 install-stubdom: mini-os-dir install-tools
 	$(MAKE) -C stubdom install
 ifeq (x86_64,$(XEN_TARGET_ARCH))
-	XEN_TARGET_ARCH=x86_32 $(MAKE) -C stubdom install-grub
+	XEN_TARGET_ARCH=x86_32 $(MAKE) -C stubdom install-grub-if-enabled
 endif
 
 .PHONY: tools/firmware/seabios-dir-force-update

stubdom/Makefile

@@ -531,6 +531,13 @@ vtpmmgr-stubdom: mini-os-$(XEN_TARGET_ARCH)-vtpmmgr vtpmmgr
 pv-grub: mini-os-$(XEN_TARGET_ARCH)-grub libxenguest grub
 	DEF_CPPFLAGS="$(TARGET_CPPFLAGS)" DEF_CFLAGS="$(TARGET_CFLAGS)" DEF_LDFLAGS="$(TARGET_LDFLAGS)" MINIOS_CONFIG="$(CURDIR)/grub/minios.cfg" $(MAKE) DESTDIR= -C $(MINI_OS) OBJ_DIR=$(CURDIR)/$< APP_OBJS=$(CURDIR)/grub-$(XEN_TARGET_ARCH)/main.a
 
+.PHONY: pv-grub-if-enabled
+ifneq ($(filter grub,$(STUBDOM_TARGETS)),)
+pv-grub-if-enabled: pv-grub
+else
+pv-grub-if-enabled:
+endif
+
 .PHONY: xenstore-stubdom
 xenstore-stubdom: mini-os-$(XEN_TARGET_ARCH)-xenstore libxenguest xenstore
 	DEF_CPPFLAGS="$(TARGET_CPPFLAGS)" DEF_CFLAGS="$(TARGET_CFLAGS)" DEF_LDFLAGS="$(TARGET_LDFLAGS)" MINIOS_CONFIG="$(CURDIR)/xenstore-minios.cfg" $(MAKE) DESTDIR= -C $(MINI_OS) OBJ_DIR=$(CURDIR)/$< APP_OBJS=$(CURDIR)/xenstore/xenstored.a
@@ -560,6 +567,12 @@ 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"
 
+ifneq ($(filter grub,$(STUBDOM_TARGETS)),)
+install-grub-if-enabled: install-grub
+else
+install-grub-if-enabled:
+endif
+
 install-c: c-stubdom
 
 install-caml: caml-stubdom