configure: restrict -ldl to where it's actually needed

This reduces overlinking of qb-blackbox.  Being a seldom used executable,
the gains are mostly theoretical, but at least this silences warnings
from some QA tools.

configure.ac

@@ -108,7 +108,10 @@ dnl it will always be "none needed", but it is not true
 dnl when linking libraries. Looks like a bug.
 AC_SEARCH_LIBS([pthread_create], [pthread])
 AC_SEARCH_LIBS([mq_open], [rt])
-AC_SEARCH_LIBS([dlopen], [dl])
+AX_SAVE_FLAGS
+AC_SEARCH_LIBS([dlopen],[dl],,[AC_MSG_ERROR([cannot find dlopen() function])])
+AC_SUBST([dlopen_LIBS],[$LIBS])
+AX_RESTORE_FLAGS
 AC_SEARCH_LIBS([socket], [socket])
 AC_SEARCH_LIBS([gethostbyname], [nsl])
 

lib/Makefile.am

@@ -40,7 +40,7 @@ source_to_lint		= util.c hdb.c ringbuffer.c ringbuffer_helper.c \
 			  map.c skiplist.c hashtable.c trie.c
 
 libqb_la_SOURCES	= $(source_to_lint) unix.c
-libqb_la_LIBADD	        = $(LTLIBOBJS)
+libqb_la_LIBADD	        = $(LTLIBOBJS) $(dlopen_LIBS)
 
 AM_LDFLAGS 	= $(LDFLAGS_COPY:-Bsymbolic-functions=)
 

m4/ax_restore_flags.m4

@@ -0,0 +1,52 @@
+# ===========================================================================
+#     http://www.gnu.org/software/autoconf-archive/ax_restore_flags.html
+# ===========================================================================
+#
+# SYNOPSIS
+#
+#   AX_RESTORE_FLAGS([namespace])
+#
+# DESCRIPTION
+#
+#   Restore common compilation flags from temporary variables.
+#
+#   Compilation flags includes: CPPFLAGS, CFLAGS, CXXFLAGS, LDFLAGS, LIBS,
+#   OBJCFLAGS.
+#
+#   By default these flags are restored to a global (empty) namespace, but
+#   user could restore from specific NAMESPACE by using
+#   AX_RESTORE_FLAGS(NAMESPACE) macro.
+#
+#   Typical usage is like:
+#
+#     AX_SAVE_FLAGS(mypackage)
+#     CPPFLAGS="-Imypackagespath ${CPPFLAGS}"
+#     dnl ... do some detection ...
+#     AX_RESTORE_FLAGS(mypackage)
+#
+# LICENSE
+#
+#   Copyright (c) 2009 Filippo Giunchedi <filippo@esaurito.net>
+#   Copyright (c) 2011 The Board of Trustees of the Leland Stanford Junior University
+#   Copyright (c) 2011 Russ Allbery <rra@stanford.edu>
+#   Copyright (c) 2013 Bastien ROUCARIES <roucaries.bastien+autoconf@gmail.com>
+#
+#   Copying and distribution of this file, with or without modification, are
+#   permitted in any medium without royalty provided the copyright notice
+#   and this notice are preserved. This file is offered as-is, without any
+#   warranty.
+
+#serial 6
+
+# save one flag in name space
+AC_DEFUN([_AX_RESTORE_ONE_FLAG],[dnl
+  AS_VAR_PUSHDEF([_ax_restore_flag_var], [$2[]_$1[]_ax_save_flags])
+  AS_VAR_COPY($2[],_ax_restore_flag_var)
+  AS_VAR_POPDEF([_ax_restore_flag_var])
+])
+
+AC_DEFUN([AX_RESTORE_FLAGS], [dnl
+   m4_foreach([FLAG], dnl
+	      [_AX_SAVE_FLAGS_LIST()], dnl
+	      [_AX_RESTORE_ONE_FLAG([$1],FLAG)])
+])

m4/ax_save_flags.m4

@@ -0,0 +1,71 @@
+# ===========================================================================
+#       http://www.gnu.org/software/autoconf-archive/ax_save_flags.html
+# ===========================================================================
+#
+# SYNOPSIS
+#
+#   AX_SAVE_FLAGS([NAMESPACE])
+#
+# DESCRIPTION
+#
+#   Save common compilation flags into temporary variables.
+#
+#   Compilation flags includes: CPPFLAGS, CFLAGS, CXXFLAGS, LDFLAGS, LIBS,
+#   OBJCFLAGS.
+#
+#   By default these flags are saved to a global (empty) namespace, but user
+#   could specify a specific NAMESPACE to AX_SAVE_FLAGS macro and latter
+#   restore it by using AX_RESTORE_FLAGS(NAMESPACE).
+#
+#     AX_SAVE_FLAGS(mypackage)
+#     CPPFLAGS="-Imypackagespath ${CPPFLAGS}"
+#     dnl .. do some detection ...
+#     AX_RESTORE_FLAGS(mypackage)
+#
+# LICENSE
+#
+#   Copyright (c) 2009 Filippo Giunchedi <filippo@esaurito.net>
+#   Copyright (c) 2011 The Board of Trustees of the Leland Stanford Junior University
+#   Copyright (c) 2011 Russ Allbery <rra@stanford.edu>
+#   Copyright (c) 2013 Bastien ROUCARIES <roucaries.bastien+autoconf@gmail.com>
+#
+#   Copying and distribution of this file, with or without modification, are
+#   permitted in any medium without royalty provided the copyright notice
+#   and this notice are preserved. This file is offered as-is, without any
+#   warranty.
+
+#serial 7
+
+# list of flag to save
+AC_DEFUN([_AX_SAVE_FLAGS_LIST],[dnl
+[CCASFLAGS],dnl
+[CFLAGS],dnl
+[CPPFLAGS],dnl
+[CXXFLAGS],dnl
+[ERLCFLAGS],dnl
+[FCFLAGS],dnl
+[FCLIBS],dnl
+[FFLAGS],dnl
+[FLIBS],dnl
+[GCJFLAGS],dnl
+[JAVACFLAGS],dnl
+[LDFLAGS],dnl
+[LIBS],dnl
+[OBJCFLAGS],dnl
+[OBJCXXFLAGS],dnl
+[UPCFLAGS],dnl
+[VALAFLAGS]dnl
+])
+
+# save one flag in name space
+AC_DEFUN([_AX_SAVE_ONE_FLAG],[
+  AS_VAR_PUSHDEF([_ax_save_flag_var], [$2[]_$1[]_ax_save_flags])
+  AS_VAR_COPY(_ax_save_flag_var, $2[])
+  AS_VAR_POPDEF([_ax_save_flag_var])
+])
+
+AC_DEFUN([AX_SAVE_FLAGS],[dnl
+   m4_foreach([FLAG], dnl
+	      [_AX_SAVE_FLAGS_LIST()], dnl
+	      [_AX_SAVE_ONE_FLAG([$1],FLAG)])
+])

tests/Makefile.am

@@ -147,6 +147,7 @@ ipc_test_LDADD += _failure_injection.la
 check_LTLIBRARIES += _failure_injection.la
 _failure_injection_la_SOURCES = _failure_injection.c _failure_injection.h
 _failure_injection_la_LDFLAGS = -module
+_failure_injection_la_LIBADD = $(dlopen_LIBS)
 endif
 
 log_test_SOURCES = check_log.c $(top_builddir)/include/qb/qblog.h