x86/mm: override stored file names for multiply built sources

To make it possible to tell apart the static symbols therein, use their
object file names instead of their source ones.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v2: Introduce __OBJECT_FILE__.

--- a/xen/Rules.mk
+++ b/xen/Rules.mk
@@ -42,10 +42,10 @@ ALL_OBJS-y               += $(BASEDIR)/x
 ALL_OBJS-y               += $(BASEDIR)/arch/$(TARGET_ARCH)/built_in.o
 ALL_OBJS-$(x86)          += $(BASEDIR)/crypto/built_in.o
 
-CFLAGS += -fno-builtin -fno-common
+CFLAGS += -nostdinc -fno-builtin -fno-common
 CFLAGS += -Werror -Wredundant-decls -Wno-pointer-arith
 CFLAGS += -pipe -g -D__XEN__ -include $(BASEDIR)/include/xen/config.h
-CFLAGS += -nostdinc
+CFLAGS += '-D__OBJECT_FILE__="$@"'
 
 CFLAGS-$(XSM_ENABLE)    += -DXSM_ENABLE
 CFLAGS-$(FLASK_ENABLE)  += -DFLASK_ENABLE
--- a/xen/arch/x86/mm/guest_walk.c
+++ b/xen/arch/x86/mm/guest_walk.c
@@ -21,6 +21,9 @@
  * along with this program; If not, see <http://www.gnu.org/licenses/>.
  */
 
+/* Allow uniquely identifying static symbols in the 3 generated objects. */
+asm(".file \"" __OBJECT_FILE__ "\"");
+
 #include <xen/types.h>
 #include <xen/mm.h>
 #include <xen/paging.h>
--- a/xen/arch/x86/mm/hap/guest_walk.c
+++ b/xen/arch/x86/mm/hap/guest_walk.c
@@ -18,6 +18,8 @@
  * this program; If not, see <http://www.gnu.org/licenses/>.
  */
 
+/* Allow uniquely identifying static symbols in the 3 generated objects. */
+asm(".file \"" __OBJECT_FILE__ "\"");
 
 #include <xen/domain_page.h>
 #include <xen/paging.h>
--- a/xen/arch/x86/mm/shadow/multi.c
+++ b/xen/arch/x86/mm/shadow/multi.c
@@ -20,7 +20,9 @@
  * along with this program; If not, see <http://www.gnu.org/licenses/>.
  */
 
-#include <xen/config.h>
+/* Allow uniquely identifying static symbols in the 3 generated objects. */
+asm(".file \"" __OBJECT_FILE__ "\"");
+
 #include <xen/types.h>
 #include <xen/mm.h>
 #include <xen/trace.h>