build: Fix missing MAKEFLAGS --no-print-directory

While we already have "--no-print-directory" added to the make flags
in some cases, there's one case where the flags is missing, when doing
an out-of-tree build with O=, e.g.
    cd xen; make O=build

Without it, we just have loads of "Entering directory" and "Leaving
directory" with the same directory.

The comment and location in the Makefile are copied from Linux.

Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

xen/Makefile

@@ -186,6 +186,11 @@ endif # root-make-done
 # We process the rest of the Makefile if this is the final invocation of make
 ifeq ($(need-sub-make),)
 
+# Do not print "Entering directory ...",
+# but we want to display it when entering to the output directory
+# so that IDEs/editors are able to understand relative filenames.
+MAKEFLAGS += --no-print-directory
+
 ifeq ($(abs_srctree),$(abs_objtree))
     # building in the source tree
     srctree := .