rules: filter out irrelevant files

It's often handy to make executables depend on each other, e.g. make a
test depend on a helper. This doesn't work now, as linker
will attempt to use the helper as an object.
To fix, filter only relevant file types before linking an executable.
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

rules.mak

@@ -102,7 +102,7 @@ LD_REL := $(CC) -nostdlib -Wl,-r
 modules:
 
 %$(EXESUF): %.o
-	$(call LINK,$^)
+	$(call LINK,$(filter %.o %.a %.mo, $^))
 
 %.a:
 	$(call quiet-command,rm -f $@ && $(AR) rcs $@ $^,"  AR    $(TARGET_DIR)$@")