Makefile.am: fix non-POSIX warning from automake

Automake issues a warning
	Makefile.am:46: warning: wildcard $(srcdir: non-POSIX variable name
	Makefile.am:46: (probably a GNU make extension)
because the GNU make function 'wildcard' is not POSIX.
Also the GNU make function 'shell' triggers a similar warning.

Use the POSIX extension '!=', that executes an arbitrary shell
command, to replace the GNU make 'wildcard'.
Don't include the file 'NEWS' because automake already includes it
by default.

Change-Id: Ice560c3789cec4f3f2197a255d6f5af7b1fde634
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/5965
Tested-by: jenkins
Reviewed-by: Jonathan McDowell <noodles-openocd@earth.li>

Makefile.am

@@ -43,13 +43,14 @@ if INTERNAL_JIMTCL
 AM_CPPFLAGS += -I$(top_srcdir)/jimtcl \
 			   -I$(top_builddir)/jimtcl
 endif
+EXTRA_DIST_NEWS != ls $(srcdir)/NEWS-*
 EXTRA_DIST += \
 	BUGS \
 	HACKING \
 	NEWTAPS \
 	README.Windows \
 	README.OSX \
-	$(wildcard $(srcdir)/NEWS*) \
+	$(EXTRA_DIST_NEWS) \
 	Doxyfile.in \
 	tools/logger.pl \
 	tools/rlink_make_speed_table \