Add a --{enable,disable}-progs configure option

Add a --{enable,disable}-progs configuration option to elfutils. This
allows to selectively disable the compilation of the elfutils programs
(in which case only the libraries are built and installed). This is
useful because the programs are often not needed, and also because
building the programs against uClibc causes several issues (lack of
obstack_printf() in uClibc for example).

Based on the former patch by Thomas Petazzoni.

[Vincent: tweak patch for 0.166]

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>

diff -rup a/configure.ac b/configure.ac
--- a/configure.ac	2016-03-31 09:48:08.000000000 +0100
+++ b/configure.ac	2016-06-17 14:47:03.561704498 +0100
@@ -253,6 +253,12 @@ AC_SUBST([LIBEBL_SUBDIR])
 AC_DEFINE_UNQUOTED(LIBEBL_SUBDIR, "$LIBEBL_SUBDIR")
 AH_TEMPLATE([LIBEBL_SUBDIR], [$libdir subdirectory containing libebl modules.])
 
+AC_ARG_ENABLE([progs],
+	AS_HELP_STRING([--enable-progs], [enable progs]),
+	enable_progs=$enableval,
+	enable_progs=yes)
+AM_CONDITIONAL(ENABLE_PROGS, test "$enable_progs" = yes)
+
 dnl zlib is mandatory.
 save_LIBS="$LIBS"
 LIBS=
diff -rup a/Makefile.am b/Makefile.am
--- a/Makefile.am	2016-01-12 12:49:19.000000000 +0000
+++ b/Makefile.am	2016-06-17 14:48:02.585861468 +0100
@@ -26,9 +26,13 @@ AM_MAKEFLAGS = --no-print-directory
 
 pkginclude_HEADERS = version.h
 
+if ENABLE_PROGS
+PROGS_SUBDIR = src
+endif
+
 # Add doc back when we have some real content.
 SUBDIRS = config m4 lib libelf libebl libdwelf libdwfl libdw libcpu libasm \
-	  backends src po tests
+	  backends $(PROGS_SUBDIR) po tests
 
 EXTRA_DIST = elfutils.spec GPG-KEY NOTES CONTRIBUTING \
 	     COPYING COPYING-GPLV2 COPYING-LGPLV3