build-sys: enable "subdir-objects" automake option

Otherwise, automake 1.14 will warn that this option will become the
default in an upcoming release, which will cause problems for the
procps-ng build.

Now that the automake rules were merged in the top level Makefile.am,
it is possible to enable "subdir-objects" without breaking the build or
the dist.

Tested that it builds and both `make check` and `make distcheck` work.

Tested that `make install` works and produces the same tree before and
after this change. Confirmed that binaries are also placed in the same
locations in the build tree.

Signed-off-by: Filipe Brandenburger <filbranden@google.com>

Makefile.am

@@ -1,5 +1,3 @@
-#AUTOMAKE_OPTIONS = subdir-objects
-
 AM_CPPFLAGS = \
 	-include $(top_builddir)/config.h \
 	-I$(top_srcdir) \

configure.ac

@@ -6,7 +6,7 @@ AC_CONFIG_MACRO_DIR([m4])
 AC_INIT([procps-ng],
 	m4_esyscmd([misc/git-version-gen .tarball-version]),
 	[procps@freelists.org],,[http://gitorious.org/procps])
-AM_INIT_AUTOMAKE([foreign 1.11 -Wall -Wno-portability tar-pax no-dist-gzip dist-xz])
+AM_INIT_AUTOMAKE([foreign 1.11 subdir-objects -Wall -Wno-portability tar-pax no-dist-gzip dist-xz])
 AM_SILENT_RULES([yes])
 AC_CONFIG_SRCDIR([free.c])
 AC_CONFIG_HEADERS([config.h])